Tree identity and diversity directly affect soil moisture and temperature but not soil carbon ten years after planting.

Soil C is the largest C pool in forest ecosystems that contributes to C sequestration and mitigates climate change. Tree diversity enhances forest productivity, so diversifying the tree species composition, notably in managed forests, could increase the quantity of organic matter being transferred to soils and alter other soil properties relevant to the C cycle.A ten-year-old tree diversity experiment was used to study the effects of tree identity and diversity (functional and taxonomic) on soils. Surface (0-10 cm) mineral soil was repeatedly measured for soil C concentration, C:N ratio, pH, moisture, and temperature in twenty-four tree species mixtures and twelve corresponding monocultures (replicated in four blocks).Soil pH, moisture, and temperature responded to tree diversity and identity. Greater productivity in above- and below-ground tree components did not increase soil C concentration. Soil pH increased and soil moisture decreased with functional diversity, more specifically, when species had different growth strategies and shade tolerances. Functional identity affected soil moisture and temperature, such that tree communities with more slow-growing and shade-tolerant species had greater soil moisture and temperature. Higher temperature was measured in communities with broadleaf-deciduous species compared to communities with coniferous-evergreen species.We conclude that long-term soil C cycling in forest plantations will likely respond to changes in soil pH, moisture, and temperature that is mediated by tree species composition, since tree species affect these soil properties through their litter quality, water uptake, and physical control of soil microclimates.

Fine-root traits in the global spectrum of plant form and function.

Plant traits determine how individual plants cope with heterogeneous environments. Despite large variability in individual traits, trait coordination and trade-offs1,2 result in some trait combinations being much more widespread than others, as revealed in the global spectrum of plant form and function (GSPFF3) and the root economics space (RES4) for aboveground and fine-root traits, respectively. Here we combine the traits that define both functional spaces. Our analysis confirms the major trends of the GSPFF and shows that the RES captures additional information. The four dimensions needed to explain the non-redundant information in the dataset can be summarized in an aboveground and a fine-root plane, corresponding to the GSPFF and the RES, respectively. Both planes display high levels of species aggregation, but the differentiation among growth forms, families and biomes is lower on the fine-root plane, which does not include any size-related trait, than on the aboveground plane. As a result, many species with similar fine-root syndromes display contrasting aboveground traits. This highlights the importance of including belowground organs to the GSPFF when exploring the interplay between different natural selection pressures and whole-plant trait integration.

Evergreenness influences fine root growth more than tree diversity in a common garden experiment.

Recent studies have reported positive net diversity effects on aboveground tree growth. However, whether similar effects occur belowground through root investment, and whether such effects are related to evergreenness of tree communities, is less clear. Here we studied vertical distribution of standing fine root biomass of twelve North American temperate tree species planted in a common garden tree diversity experiment of varying species richness and evergreenness to test whether belowground niche complementarity of trees could explain positive diversity effects reported aboveground. We tested two alternative hypotheses: trees in mixtures increase uptake of soil resources (1) by increasing vertical root stratification and/or producing a greater fine root density (mg cm-3) or (2) by producing similar or fewer fine roots that are potentially more efficient. Additionally, we hypothesized that proportional allocation to belowground biomass increases with evergreenness of tree communities. Fine roots were sampled in six layers of 5-10 cm, from 0 to 40 cm depth in single-, two- and four-species mixtures. We did not observe an effect of species richness on rooting depth or root density, refuting the hypothesis that aboveground overyielding in tree mixtures is linked to fine root overyielding. Rather, we observed a significant negative diversity effect (- 7.6%) on total fine root density, suggesting overall less investment to fine roots with increasing diversity. The strong positive effect of evergreeness on proportional allocation to fine roots over aboveground parts suggests that deciduous tree roots may be generally more efficient at absorbing soil resources, at least in the early years after tree establishment.

The relative weight of ontogeny, topology and climate in the architectural development of three North American conifers.

Knowledge of plant architecture allows retrospective study of plant development, hence provides powerful tools, through modelling and simulation, to link this development with environmental constraints, and then predict its response to global change. The present study aims to determine some of the main endogenous and exogenous variables driving the architectural development of three North American conifers. We measured architectural traits retrospectively on the trunk, branches and twigs of whole tree crowns for each species: annual shoot length (ASL), needle length, branching patterns and reproduction organs (male and female). We fitted a partial least square (PLS) regression to explain each architectural trait with respect to topological, ontogenic and climatic variables. Results showed a significant weight of these three groups of variables for previous and current year, corresponding, respectively, to organogenesis and elongation. Topological and ontogenic variables had the greatest weight in models. Particularly, all architectural traits were strongly correlated with ASL. We highlighted a negative architectural response of two species to higher than average temperatures, whereas the third one took advantage of these higher temperatures to some degree. Tree architectural development weekly but significantly improved with higher precipitation. Our study underlines the strong weight of topology and ontogeny in tree growth patterns at twig and branch scales. The correlation between ASL and other tree architectural traits should be integrated into architectural development models. Climate variables are secondary in importance at the twig scale. However, interannual climate variations influence all axis categories and branching orders and therefore significantly impact crown development as a whole. This latter impact may increase with climate change, especially as climate affects architectural traits over at least 2 years, through organogenesis and elongation.

Do temperate tree species diversity and identity influence soil microbial community function and composition?

Studies of biodiversity-ecosystem function in treed ecosystems have generally focused on aboveground functions. This study investigates intertrophic links between tree diversity and soil microbial community function and composition. We examined how microbial communities in surface mineral soil responded to experimental gradients of tree species richness (SR), functional diversity (FD), community-weighted mean trait value (CWM), and tree identity. The site was a 4-year-old common garden experiment near Montreal, Canada, consisting of deciduous and evergreen tree species mixtures. Microbial community composition, community-level physiological profiles, and respiration were evaluated using phospholipid fatty acid (PLFA) analysis and the MicroResp™ system, respectively. The relationship between tree species richness and glucose-induced respiration (GIR), basal respiration (BR), metabolic quotient (qCO 2) followed a positive but saturating shape. Microbial communities associated with species mixtures were more active (basal respiration [BR]), with higher biomass (glucose-induced respiration [GIR]), and used a greater number of carbon sources than monocultures. Communities associated with deciduous tree species used a greater number of carbon sources than those associated with evergreen species, suggesting a greater soil carbon storage capacity. There were no differences in microbial composition (PLFA) between monocultures and SR mixtures. The FD and the CWM of several functional traits affected both BR and GIR. In general, the CWM of traits had stronger effects than did FD, suggesting that certain traits of dominant species have more effect on ecosystem processes than does FD. Both the functions of GIR and BR were positively related to aboveground tree community productivity. Both tree diversity (SR) and identity (species and functional identity-leaf habit) affected soil microbial community respiration, biomass, and composition. For the first time, we identified functional traits related to life-history strategy, as well as root traits that influence another trophic level, soil microbial community function, via effects on BR and GIR.

The inhibition of ammonium uptake in excised birch (Betula pendula) roots by batatasin-III.

In northern Sweden, plants growing in association with the clonal dwarf shrub Empetrum hermaphroditum usually exhibit limited growth and are N-depleted. Previous studies suggest that this negative effect by E. hermaphroditum may be explained, at least in part, by the release of phenolic compounds, particularly the dihydrostilbene, batatasin-III from foliage to soil. In the present work, we investigated whether batatasin-III has the potential to interfere with NH4+ uptake in birch (Betula pendula) roots. Excised birch roots were exposed to batatasin-III during brief periods in 15NH4+ solutions, and then analyzed for labeled N. Batatasin-III inhibited N-NH4+ uptake by 28, 89 and 95% compared with the control, when roots were treated with 0.1, 1.0 and 2.8 mM of batatasin-III, respectively. The effect of 1.0-mM batatasin-III was greater at pH 4.2 than at pH 6.8. In addition, the inhibition of N-NH4+ uptake by batatasin-III was not reversed after rinsing the roots in water and transferring them to a batatasin-III free solution. Furthermore, birch seedlings immersed in a 1.0-mM batatasin-III solution for 2 h, and then replanted in pots with soil, had decreased growth, such that 10 weeks after treatment, the dry mass of both shoots and roots was reduced by 74 and 73%, respectively, compared with control seedlings. This suggests that a brief exposure to batatasin-III may have a long-term inhibitory effect on whole plant growth. Using plasma membrane vesicles isolated from easily extractable spinach (Spinacia oleracea) leaves, it was found that batatasin-III strongly inhibited proton pumping in isolated plasma membrane vesicles, while it only slightly inhibited ATP hydrolytic activity. The uncoupling of proton pumping from ATP hydrolytic activity suggests that batatasin-III disturbs membrane integrity. This hypothesis was further supported by a greater efflux of ions from birch roots immersed in a batatasin-III solution than from roots in a control solution.