Precipitation-induced biomass enhancement and differential allocation in Inner Mongolia's herbaceous and shrub communities.

Changes in precipitation patterns induced by global climate change have profound implications for the structure and function of grassland ecosystems. However, the relationship between plant diversity and ecosystem function across different grassland types, particularly those with varying plant compositions and dominant species, remains inadequately understood. To address this knowledge gap, a five-year experimental manipulation of precipitation was conducted within herbaceous and shrub communities in the desert grasslands of Inner Mongolia. We found that increased precipitation significantly enhances aboveground biomass (AGB), belowground biomass (BGB), and community total biomass (CTB) in both herbaceous and shrub communities. In herbaceous communities, increased precipitation led to a disproportionate increase in both aboveground and belowground biomass, supporting the optimal allocation hypothesis. Structural equation modeling (SEM) further elucidated that precipitation regulates AGB and CTB through species richness and functional traits in herbaceous communities. In shrub communities, precipitation influences AGB, BGB, and CTB by affecting species richness and soil water content. This study highlights the critical role of precipitation in shaping biomass dynamics and allocation strategies within herbaceous and shrub communities in desert steppe of Inner Mongolia. These findings provide essential insights into the potential responses of desert grassland ecosystems to ongoing climate change.

Root and biomass allocation traits predict changes in plant species and communities over four decades of global change.

Global change is affecting the distribution and population dynamics of plant species across the planet, leading to trends such as shifts in distribution toward the poles and to higher elevations. Yet, we poorly understand why individual species respond differently to warming and other environmental changes, or how the trait composition of communities responds. Here we ask two questions regarding plant species and community changes over 42 years of global change in a temperate montane forest in Québec, Canada: (1) How did the trait composition, alpha diversity, and beta diversity of understory vascular plant communities change between 1970 and 2010, a period over which the region experienced 1.5°C of warming and changes in nitrogen deposition? (2) Can traits predict shifts in species elevation and abundance over this time period? For 46 understory vascular species, we locally measured six aboveground traits, and for 36 of those (not including shrubs), we also measured five belowground traits. Collectively, they capture leading dimensions of phenotypic variation that are associated with climatic and resource niches. At the community level, the trait composition of high-elevation plots shifted, primarily for two root traits: specific root length decreased and rooting depth increased. The mean trait values of high-elevation plots shifted over time toward values initially associated with low-elevation plots. These changes led to trait homogenization across elevations. The community-level shifts in traits mirrored the taxonomic shifts reported elsewhere for this site. At the species level, two of the three traits predicting changes in species elevation and abundance were belowground traits (low mycorrhizal fraction and shallow rooting). These findings highlight the importance of root traits, which, along with leaf mass fraction, were associated with shifts in distribution and abundance over four decades. Community-level trait changes were largely similar across the elevational and temporal gradients. In contrast, traits typically associated with lower elevations at the community level did not predict differences among species in their shift in abundance or distribution, indicating a decoupling between species- and community-level responses. Overall, changes were consistent with some influence of both climate warming and increased nitrogen availability.

The root strategy of the C4 grasses tends to be 'do-it-yourself'.

Root resource acquisition strategies play a crucial role in understanding plant water uptake and drought adaptation. However, the interrelationships among mycorrhizal associations, root hair development, and fine root strategies, as well as the disparities between C3 and C4 grasses, remain largely unknown. A pot experiment was conducted to determine leaf gas exchange, root morphology, root hair, mycorrhizal fungi, and biomass allocation of three C4 grasses and four C3 grasses, common species of grasslands in Northeast China, under the control and drought conditions. Compared to the C3 grasses, the C4 grasses increased specific surface area by decreasing tissue density, yet exhibited root hair factor at only 21 % of the C3 grasses. Under the drought conditions, the C4 grasses exhibited more intense and extensive adjustments in root traits, characterized by shifts toward a more conservative morphology with increased root diameter and tissue density, as well as reduced mycorrhizal colonization rates. These adaptations led to a decrease in root absorptive function, which was compensated in the C4 grasses by greater root biomass partitioning and root hair factor. Variances in root strategies between plants functional groups were closely related to leaf photosynthetic rate, water and nitrogen use efficiency. We observed that the C4 grasses prefer direct acquisition of soil resources through the fine root pathway over the root hair or mycorrhizal pathway, suggesting a 'do-it-yourself' approach. These findings provide valuable insights into how plant communities of different photosynthetic types might respond to future climate change.

Early overyielding in a mixed deciduous forest is driven by both above- and below ground species-specific acclimation.

BACKGROUND AND AIMS: Mixed forest plantations are increasingly recognised for their role in mitigating the impacts of climate change and enhancing ecosystem resilience. Yet, there remains a significant gap in understanding the early-stage dynamics of species trait diversity and interspecies interactions, particularly in pure deciduous mixtures. This study aims to explore the timing and mechanisms by which trait diversity of deciduous species and competitive interactions influence yield, carbon allocation, and space occupation in mixed forests, both above- and belowground. METHODS: A forest inventory was conducted in planted monocultures, 2-species, and 4-species mixtures of European Acer, Tilia, Carpinus, and Quercus, representing a spectrum from acquisitive to conservative tree species. Competition effects were assessed with linear mixed-effects models at the level of biomass and space acquisition, including leaf, canopy, stem, and fine root traits. KEY RESULTS: Early aboveground growth effects were observed six years post-planting, with significant biomass accumulation after eight years, strongly influenced by species composition. Mixtures, especially with acquisitive species, exhibited aboveground overyielding, 1.5- to 1.9-times higher than monocultures. Fine roots showed substantial overyielding in high diversity stands. Biomass allocation was species-specific and varied markedly by tree size, the level of diversity, and between acquisitive Acer and the more conservative species. No root segregation was found. CONCLUSIONS: Our findings underscore the critical role of species trait diversity in enhancing productivity in mixed deciduous forest plantations. Allometric changes highlight the need to differentiate between (active) acclimations and (passive) tree size-related changes, but illustrate major consequences of competitive interactions for the functional relation between leaves, stem, and roots. This study points towards the significant contributions of both above- and belowground components to overall productivity of planted mixed-species forests.

Effects of plant nutrient acquisition strategies on biomass allocation patterns in wetlands along successional sequences in the semi-arid upper Yellow River basin.

The ecological environment of wetlands in semi-arid regions has deteriorated, and vegetation succession has accelerated due to climate warming-induced aridification and human interference. The nutrient acquisition strategies and biomass allocation patterns reflect plant growth strategies in response to environmental changes. However, the impact of nutrient acquisition strategies on biomass allocation in successional vegetation remains unclear. We investigated 87 plant communities from 13 wetland sites in the semi-arid upper Yellow River basin. These communities were divided into three successional sequences: the herbaceous community (HC), the herbaceous-shrub mixed community (HSC), and the shrub community (SC). The nutrient composition of stems and leaves, as well as the biomass distribution above and belowground, were investigated. Results revealed that aboveground biomass increased with succession while belowground biomass decreased. Specifically, SC exhibited the highest stem biomass of 1,194.53 g m-2, while HC had the highest belowground biomass of 2,054.37 g m-2. Additionally, significant positive correlations were observed between leaf and stem biomasses in both HC and SC. The nitrogen (N) and phosphorus (P) contents within aboveground parts displayed an evident upward trend along the succession sequence. The highest N and P contents were found in SC, followed by HSC, and the lowest in HC. Stem N was negatively correlated with stem, leaf, and belowground biomass but positively correlated with root-shoot ratio. Leaf P displayed positive correlations with aboveground biomass while showing negative correlations with belowground biomass and root-shoot ratio. The ratios of C:N, C:P, and N:P in stem and leaf exhibited positive correlations with belowground biomass. The random forest model further demonstrated that stem N and leaf P exerted significant effects on aboveground biomass, while leaf P, stem N and P, and leaf C:P ratio had significant effects on belowground components. Additionally, the root-shoot ratio was significantly influenced by leaf P, leaf C:P ratio, and stem N, P, and C:P ratio. Therefore, the aboveground and belowground biomasses exhibited asynchronism across successional sequences, while plant nutrient acquisition strategies, involving nutrient levels and stoichiometric ratios, determined the biomass allocation pattern. This study offers valuable insights for assessing vegetation adaptability and formulating restoration plans in the semi-arid upper Yellow River basin.

Alpine grassland community productivity and diversity differences influence significantly plant sexual reproduction strategies.

Whether and how community structure variation affects plant sexual reproduction is crucial for understanding species' local adaptation and plant community assembly, but remains unrevealed. In Qinghai-Tibetan grassland communities that differed in aboveground biomass (AGB) and species diversity, we found significant influence of AGB on both species' reproductive biomass allocation (RBA) and flowering and fruiting time, but of species diversity only on species' reproductive time. In high-AGB or high-diversity communities, smaller and earlier flowering species generally advanced their reproductive phenology and increased their reproductive allocation for maximizing their reproductive success, whereas larger and later flowering species delayed their reproductive phenology and decreased their reproductive allocation for maximizing their vegetative growth and resource competition. This change in reproductive allocation with the variation in community structures was more pronounced in nonclonal as compared to clonal plant species. Thus, we evidence an important influence of community structure on plant sexual reproduction strategies, and the pattern of the influence depends largely on species biological attributes.

Environmental aridity driving latitudinal pattern of biomass allocation fractions in root systems of 63 shrub species in dry valleys.

Fine roots and absorptive roots play key roles in acquiring resources throughout soil profiles and determining plant functions along environmental gradients. Yet, the geographical pattern of carbon allocation in fine roots, particularly in absorptive roots, and their relations with plant sizes and evironment are less understood. We sampled 243 xerophytic shrubs from 63 species distributed along the latitudinal gradient (23°N to 32°N) in dry valleys of southwest China and synthetically measured biomass fractions of plant organs, especially fine roots and absorptive roots (1st to 3rd root order). We identified latitudinal patterns of biomass allocation fractions of organs and their relationships with plant sizes and environmental factors. The latitudinal patterns of both absorptive root and fine-root fractions followed weak unimodal distributions; stem biomass fraction increased with the latitude, while the leaf biomass fraction decreased. The fraction of fine-root biomass had negative relationships with plant height and root depth. The fractions of root, fine root, and absorptive root biomass were largely explained by soil moisture. Furthermore, fraction of fine-root biomass increased in a relatively humid environment. Overall, soil moisture was the most important factor in driving latitudinal patterns of biomass fraction. Our study highlighted that functional redistribution of root system biomass was the critical adaptive strategy along a latitudinal gradient.

The curvilinear responses of biomass accumulation and root morphology to a soil salt-nitrogen environment reflect the phytodesalination capability of the euhalophyte Suaeda salsa L.

Under the sufficient nitrogen supply, it is of great significance to investigate the law of biomass allocation, root morphological traits, and the salt absorption capacity of euhalophytes to evaluate their biological desalination in saline soil. Although the curvilinear responses of biomass accumulation and root morphology in response to soil salinity have been recognized, these perceptions are still confined to the descriptions of inter-treatment population changes and lack details on biomass allocation in organs at an individual level. In this study, Suaeda salsa was grown in root boxes across a range of soil salt levels. The study showed that their growth and development were significantly affected by soil soluble salts. The law of biomass allocation was described as follows: increased soil soluble salts significantly increased the leaf mass ratio and decreased the stem mass ratio, and slightly increased the root mass ratio among treatments. For individuals at each treatment, leaf mass ratio > stem mass ratio > root mass ratio, except in the control treatment at the flower bud and fruit stages. Biomass responses of the control treatment indicated that salt was not rigorously required for Suaeda salsa in the presence of an adequate nitrogen supply, as verified by the correlation between biomass, nitrogen, and soil soluble salt. Salt could significantly inhibit the growth of Suaeda salsa (P<0.01), whereas nitrogen could significantly promote its growth (P<0.01). Root morphology in response to soil soluble salts showed that salt acquisition by the root was highest at a salt level of 0.70%, which corresponds to light saline soil. Consequently, we conclude that phytodesalination by Suaeda salsa was optimal in the light saline soil, followed by moderate saline soil.

Effects of kinship and integration between adjacent/non-adjacent ramets on the growth and feedback with soil biota in a clonal invader.

Many invasive plants can reproduce through both seeds and clonal growth. In habitats, interacting seedlings may originate from the same mother, and interacting ramets originating from the same plant may not be adjacent to each other in the stolon, particularly for vines that can show curved growth. However, in a homogeneous environment, how kinship and integration between adjacent/non-adjacent ramets affect plant growth and feedback with soil biota has been less studied. We address these questions using an invasive stoloniferous vine Mikania micrantha. We found that sibling groups and stranger groups did not differ in biomass production, root allocation and feedback with soil biota, indicating that kin recognition is unlikely in M. micrantha. For two-ramet stolon fragments in which interacting ramets were adjacent to each other, older ramets allocated more biomass to roots than younger ramets when integrated, particularly in comparison with disconnected ramets from different genotypes, indicating that a division of labor was induced. For four-ramet stolon fragments in which there were two unrooted ramets between the two rooted, interacting ramets, integration increased biomass allocation to roots, possibly because only two of the four ramets could absorb belowground resources and a lower shoot allocation decreased aboveground light competition. When inoculated with soil biota conditioned by the four-ramet integrated fragments, plants of M. micrantha also increased biomass allocation to roots. These results indicate that the distance between interacting ramets in the stolon may affect the integration effect and feedback with soil biota in clonal plants.

Mycorrhization enhances plant growth and stabilizes biomass allocation under drought.

Plants and their symbionts, such as arbuscular mycorrhizal (AM) fungi, are increasingly subjected to various environmental stressors due to climate change, including drought. As a response to drought, plants generally allocate more biomass to roots over shoots, thereby facilitating water uptake. However, whether this biomass allocation shift is modulated by AM fungi remains unknown. Based on 5691 paired observations from 154 plant species, we conducted a meta-analysis to evaluate how AM fungi modulate the responses of plant growth and biomass allocation (e.g., root-to-shoot ratio, R/S) to drought. We found that AM fungi attenuate the negative impact of drought on plant growth, including biomass production, photosynthetic performance and resource (e.g. nutrient and water) uptake. Accordingly, drought significantly increased R/S in non-inoculated plants, but not in plants symbiotic with established AM fungal symbioses. These results suggest that AM fungi promote plant growth and stabilize their R/S through facilitating nutrient and water uptake in plants under drought. Our findings highlight the crucial role of AM fungi in enhancing plant resilience to drought by optimizing resource allocation. This knowledge opens avenues for sustainable agricultural practices that leverage symbiotic relationships for climate adaptation.

Influence of tree size on the scaling relationships of lamina and petiole traits: A case study using Camptotheca acuminata Decne.

There is a lack of research on whether tree size affects lamina and petiole biomass allocation patterns, whereas the trade-off between leaf biomass allocated to the lamina and the petiole is of significance when considering the hydraulic and mechanical function of the leaf as a whole. Here, Camptotheca acuminata Decne was selected for study because of the availability of trees differing in size growing under the same conditions. A total of 600 leaves for two tree size groups and 300 leaves per group differing in height and trunk diameter were collected. The lamina fresh mass (LFM), lamina dry mass (LDM), lamina area (LA), petiole fresh mass (PFM), and petiole length (PL) of each leaf was measured, and reduced major axis regression protocols were used to determine the scaling relationships among the five functional traits. The bootstrap percentile method was used to determine if the scaling exponents of the traits differed significantly between the two tree size groups. The results indicated that (i) there was a significant difference in the LFM, LDM, PFM, PL, LMA, LFMA and PFM/LFM between large and small trees, but no significant difference in LA; (ii) the LA versus LFM, LA versus LDM, LFM versus PFM, LA versus PFM, and PL versus PFM scaling relationships of the two groups were allometric (i.e., not isometric); (iii) there were significant differences in the scaling exponents of LA versus LFM, LA versus PFM, PL versus PFM between the two groups, but there was no significant difference in the LFM versus PFM scaling relationship between the two groups of trees. The data were also consistent with the phenomenon known as "diminishing returns". These data indicate that tree size influences leaf biomass allocation patterns in ways that can potentially influence overall plant growth, and therefore have an important bearing on life-history strategies.

More diverse rhizobial communities can lead to higher symbiotic nitrogen fixation rates, even in nitrogen-rich soils.

Symbiotic nitrogen (N) fixation (SNF) by legumes and their rhizobial partners is one of the most important sources of bioavailable N to terrestrial ecosystems. While most work on the regulation of SNF has focussed on abiotic drivers such as light, water and soil nutrients, the diversity of rhizobia with which individual legume partners may play an important but under-recognized role in regulating N inputs from SNF. By experimentally manipulating the diversity of rhizobia available to legumes, we demonstrate that rhizobial diversity can increase average SNF rates by more than 90%, and that high rhizobial diversity can induce increased SNF even under conditions of high soil N fertilization. However, the effects of rhizobial diversity, the conditions under which diversity effects were the strongest, and the likely mechanisms driving these diversity effects differed between the two legume species we assessed. These results provide evidence that biodiversity-ecosystem function relationships can occur at the scales of an individual plant and that the effects of rhizobial diversity may be as important as long-established abiotic factors, such as N availability, in driving terrestrial N inputs via SNF.

Understanding mechanistic variability in physiological and biochemical responses of pea cultivars (Pisum sativum L.) to ozone exposure.

Increasing concentration of ground level O3 and its negative impacts on agricultural output is well documented, however, the response of leguminous crop plants is still sparsely cited. Given their nutritional richness, legume seeds are widely esteemed as a crucial dietary staple worldwide, prized for their abundance of oil, protein, dietary fiber, and low-fat characteristics. Termed as the "poor man's meat" due to their high-quality protein, they hold immense economic value. Acknowledging the significance of legumes, a field experiment was conducted to understand the physiological and antioxidant responses, stomatal characteristics, and yield response in three cultivars of Pisum sativum L. (K Agaiti, K Uday and K Damini), exposed to elevated ozone (O3). In the present study, Pisum sativum cultivars were subjected to ambient (control) and elevated (+15 ppb) concentrations of O3, using separate sets of OTCs. Elevated O3 stimulated the activity of the enzymes of Halliwell Asada pathway, which were responsible for the differential response of the three experimental cultivars. While K Agaiti and K Uday focused on upregulating their antioxidant defense, K Damini followed the strategy of biomass allocation. Test weight showed that K Damini was most efficient in succoring the yield losses under elevated O3. Under elevated O3, test weight reduced by 8.91%, 7.52%, and 5.1%, respectively, in K Agaiti, followed by K Uday and K Damini, rendering K Agaiti most sensitive to O3 stress. The present study not only helps us to elucidate the O3 sensitivity of the selected experimental cultivars, it also helps us in screening O3 tolerant cultivars for future agricultural practices.

Responses of non-native and native plant species to fluctuations of water availability in a greenhouse experiment.

Water availability strongly influences the survival, growth, and reproduction of most terrestrial plant species. Experimental evidence has well documented the effect of changes in total amount of water availability on non-native vs. native plants. However, little is known about how fluctuations in water availability affect these two groups, although more extreme fluctuations in water availability increasingly occur with prolonged drought and extreme precipitation events. Here, we grew seven non-native and seven native plant species individually in the greenhouse. Then, we exposed them to four watering treatments, each treatment with the same total amount of water, but with different divisions: W1 (added water 16 times with 125 mL per time), W2 (8 times, 250 mL per time), W3 (4 times, 500 mL per time), and W4 (2 times, 1000 mL per time). We found that both non-native and native plants produced the most biomass under medium frequency/magnitude watering treatments (W2 and W3). Interestingly, non-native plants produced 34% more biomass with the infrequent, substantial watering treatment (W4) than with frequent, minor watering treatment (W1), whereas native plants showed opposite patterns, producing 26% more biomass with W1 than with W4. Differences in the ratio of root to shoot under few/large and many/small watering treatments of non-native vs. native species probably contributed to their different responses in biomass production. Our results advance the current understanding of the effect of water availability on non-native plants, which are affected not only by changes in amount of water availability but also by fluctuations in water availability. Furthermore, our results indicate that an increased few/large precipitation pattern expected under climate change conditions might further promote non-native plant invasions. Future field experiments with multiple phylogenetically controlled pairs of non-native and native species will be required to enhance our understanding of how water availability fluctuations impact on non-native invasions.

Different ectomycorrhizal fungal species impact poplar growth but not phosphorus utilization under low P supply.

Tree growth is often limited by phosphorus (P) availability. The trade-off between P homeostasis and growth is unknown. Ectomycorrhizal fungi (EMF) facilitate P availability but this trait varies among different fungal species and isolates. Here, we tested the hypotheses that (i) colonization with EMF boosts plant growth under P-limited conditions and that (ii) the poplars show P homeostasis because increased P uptake is used for growth and not for P accumulation in the tissues. We used two P treatments (high phosphate [HP]: 64 µM Pi, low phosphate [LP]: 0.64 µM Pi in the nutrient solution) and four fungal treatments (Paxillus involutus MAJ, Paxillus involutus NAU, Laccaria bicolor dikaryon LBD, Laccaria bicolor monokaryon LBM) in addition to non-inoculated poplar plants (NI) to measure growth, biomass, gas exchange and P contents. High phosphate (HP) stimulated growth compared with LP conditions. Poplars colonized with MAJ, NAU and NI showed higher growth and biomass production than those with LBD or LBM. Photosynthesis rates of poplars with lower biomass production were similar to or higher than those of plants with higher growth rates. The tissue concentrations of P were higher under HP than LP conditions and rarely affected by ectomycorrhizal colonization. Under LP, the plants produced 44% greater biomass per unit of P than under HP. At a given P supply, the tissue concentration was stable irrespective of the growth rate indicating P homeostasis. Laccaria bicolor caused growth inhibition, irrespective of P availability. These results suggest that in young poplars distinct species-specific ectomycorrhizal traits overshadowed potential growth benefits.

Effects of different sowing dates on biomass allocation of various organs and allometric growth of Fagopyrum esculentum.

Introduction: The sowing date plays a crucial role in influencing the growth and reproduction of plants, with its specific impact on biomass allocation and allometric growth remaining unclear. Understanding these effects is essential for optimizing agricultural practices and enhancing crop productivity. Methods: To investigate the effects of sowing dates on biomass allocation and allometric growth, a field experiment was conducted with sequential sowings of Fagopyrum esculentum from April 12th to August 11th in 2018. Biomass measurements were taken across various plant organs, and corresponding allocation calculations were made. A detailed analysis of the allometric growth relationship involving organ biomass variations was performed. Results: The study revealed that the accumulation and allocation of organ biomass in buckwheat were significantly impacted by the sowing dates. Delayed planting led to reduced vegetative growth and increased biomass allocation towards reproduction. Allometric parameters such as exponent, constant, and individual size of buckwheat were notably affected by delayed planting. Interestingly, the allometric exponents governing the relationships between reproductive vs. vegetative biomass and belowground vs. aboveground biomass exhibited varying trends across different sowing dates. Discussion: Notably, late sowings resulted in significantly higher reproductive biomass compared to early and middle sowings. These findings highlight the nuanced relationship between plant size and reproductive biomass under different sowing dates, emphasizing the critical role of planting timing in shaping mature plant sizes and reproductive outcomes. The study underscores the importance of considering sowing dates in agricultural practices to optimize plant growth and productivity.

Changes in above- versus belowground biomass distribution in permafrost regions in response to climate warming.

Permafrost regions contain approximately half of the carbon stored in land ecosystems and have warmed at least twice as much as any other biome. This warming has influenced vegetation activity, leading to changes in plant composition, physiology, and biomass storage in aboveground and belowground components, ultimately impacting ecosystem carbon balance. Yet, little is known about the causes and magnitude of long-term changes in the above- to belowground biomass ratio of plants (η). Here, we analyzed η values using 3,013 plots and 26,337 species-specific measurements across eight sites on the Tibetan Plateau from 1995 to 2021. Our analysis revealed distinct temporal trends in η for three vegetation types: a 17% increase in alpine wetlands, and a decrease of 26% and 48% in alpine meadows and alpine steppes, respectively. These trends were primarily driven by temperature-induced growth preferences rather than shifts in plant species composition. Our findings indicate that in wetter ecosystems, climate warming promotes aboveground plant growth, while in drier ecosystems, such as alpine meadows and alpine steppes, plants allocate more biomass belowground. Furthermore, we observed a threefold strengthening of the warming effect on η over the past 27 y. Soil moisture was found to modulate the sensitivity of η to soil temperature in alpine meadows and alpine steppes, but not in alpine wetlands. Our results contribute to a better understanding of the processes driving the response of biomass distribution to climate warming, which is crucial for predicting the future carbon trajectory of permafrost ecosystems and climate feedback.

Evolutionary pathways to lower biomass allocation to the seed coat in crops: insights from allometric scaling.

Crops generally have seeds larger than their wild progenitors´ and with reduced dormancy. In wild plants, seed mass and allocation to the seed coat (a proxy for physical dormancy) scale allometrically so that larger seeds tend to allocate less to the coats. Larger seeds and lightweight coats might thus have evolved as correlated traits in crops. We tested whether 34 crops and 22 of their wild progenitors fit the allometry described in the literature, which would indicate co-selection of both traits during crop evolution. Deviations from the allometry would suggest that other evolutionary processes contribute to explain the emergence of larger, lightweight-coated seeds in crops. Crops fitted the scaling slope but deviated from its intercept in a consistent way: Seed coats of crops were lighter than expected by their seed size. The wild progenitors of crops displayed the same trend, indicating that deviations cannot be solely attributed to artificial selection during or after domestication. The evolution of seeds with small coats in crops likely resulted from a combination of various pressures, including the selection of wild progenitors with coats smaller than other wild plants, further decreases during early evolution under cultivation, and indirect selection due to the seed coat-seed size allometry.

Elevated CO2 concentration enhance carbon and nitrogen metabolism and biomass accumulation of Ormosiahosiei.

Elevated CO2 concentrations may inhibit photosynthesis due to nitrogen deficiency, but legumes may be able to overcome this limitation and continue to grow. Our study confirms this conjecture well. First, we placed the two-year-old potted saplings of Ormosia hosiei (O. hosiei) (a leguminous tree species) in the open-top chamber (OTC) with three CO2 concentrations of 400 (CK), 600 (E1), and 800 µmol·mol-1 (E2) to simulate the elevated CO2 concentration environment. After 146 days, the light saturation point (LSP), light compensation point (LCP), apparent quantum efficiency (AQE), and dark respiration rate (Rd) of O. hosiei were increased under increasing CO2 concentration and obtain the maximum ribulose diphosphate (RuBP) carboxylation rate (Vc max) and RuBP regenerated photosynthetic electron transfer rate (Jmax) were also significantly increased under E2 treatment (P < 0.05). This results in a significant increase of the maximum assimilation rate (Amax) under elevated CO2 concentrations. Sucrose phosphate synthase (SPS) activity in sucrose metabolism increased in the leaves, more soluble sugars, starches, and sucrose was produced, but sucrose content only in leaves increased at E2, and more carbon flows to the roots. The activity of the NH4+ assimilating enzymes glutamine synthetase (GS), glutamate synthetase (GOGAT), and glutamate dehydrogenase (GDH) in the leaves of O. hosiei increases under elevated CO2 concentrations to promote nitrogen synthesis that reduces the content of ammonium nitrogen and increases the content of nitrate nitrogen. In addition, under E1 conditions, sucrose synthase (SS), direction of synthesis activity was highest and sucrose invertase (INV) activity was lowest, this means that the balance of C and N metabolism is maintained. While under E2 conditions SS activity decreased and INV activity increased, this increased C/N and nitrogen use efficiency. So, the elevated CO2 concentration promotes the accumulation of O. hosiei biomass, especially in the aboveground part, but did not have a significant effect on the accumulation of root biomass. This means that O. hosiei is able to cope under the elevated CO2 concentration without showing photosynthetic adaptation during the experimental period.

Responses of stem growth and canopy greenness of temperate conifers to dry spells.

Dry spells strongly influence biomass production in forest ecosystems. Their effects may last several years following a drought event, prolonging growth reduction and therefore restricting carbon sequestration. Yet, our understanding of the impact of dry spells on the vitality of trees' above-ground biomass components (e.g., stems and leaves) at a landscape level remains limited. We analyzed the responses of Pinus sylvestris and Picea abies to the four most severe drought years in topographically complex sites. To represent stem growth and canopy greenness, we used chronologies of tree-ring width and time series of the Normalized Difference Vegetation Index (NDVI). We analyzed the responses of radial tree growth and NDVI to dry spells using superposed epoch analysis and further explored this relationship using mixed-effect models. Our results show a stronger and more persistent response of radial growth to dry spells and faster recovery of canopy greenness. Canopy greenness started to recover the year after the dry spell, whereas radial tree growth remained reduced for the two subsequent years and did not recover the pre-drought level until the fourth year after the event. Stem growth and canopy greenness were influenced by climatic conditions during and after drought events, while the effect of topography was marginal. The opposite responses of stem growth and canopy greenness following drought events suggest a different impact of dry spells on trees´ sink and source compartments. These results underscore the crucial importance of understanding the complexities of tree growth as a major sink of atmospheric carbon.