Leaf Traits Explain the Growth Variation and Nitrogen Response of Eucalyptus urophylla × Eucalyptus grandis and Dalbergia odorifera in Mixed Culture.

Mixed cultivation with legumes may alleviate the nitrogen (N) limitation of monoculture Eucalyptus. However, how leaf functional traits respond to N in mixed cultivation with legumes and how they affect tree growth are unclear. Thus, this study investigated the response of leaf functional traits of Eucalyptus urophylla × Eucalyptus grandis (E. urophylla × E. grandis) and Dalbergia odorifera (D. odorifera) to mixed culture and N application, as well as the regulatory pathways of key traits on seedling growth. In this study, a pot-controlled experiment was set up, and seedling growth indicators, leaf physiology, morphological parameters, and N content were collected and analyzed after 180 days of N application treatment. The results indicated that mixed culture improved the N absorption and photosynthetic rate of E. urophylla × E. grandis, further promoting seedling growth but inhibiting the photosynthetic process of D. odorifera, reducing its growth and biomass. Redundancy analysis and path analysis revealed that leaf nitrogen content, pigment content, and photosynthesis-related physiological indicators were the traits most directly related to seedling growth and biomass accumulation, with the net photosynthetic rate explaining 50.9% and 55.8% of the variation in growth indicators for E. urophylla × E. grandis and D. odorifera, respectively. Additionally, leaf morphological traits are related to the trade-off strategy exhibited by E. urophylla × E. grandis and D. odorifera based on N competition. This study demonstrated that physiological traits related to photosynthesis are reliable predictors of N nutrition and tree growth in mixed stands, while leaf morphological traits reflect the resource trade-off strategies of different tree species.

Effects of Elevated Aluminum Concentration and Distribution on Root Damage, Cell Wall Polysaccharides, and Nutrient Uptake in Different Tolerant Eucalyptus Clones.

Aluminized acidic soil can damage Eucalyptus roots and limit tree growth, hindering the productivity of Eucalyptus plantations. At present, the negative impacts of elevated aluminum (Al) on the cell morphology and cell wall properties of Eucalyptus root tip are still unclear. In order to investigate the responses of two different tolerant clones, Eucalyptus urophylla (G4) and Eucalyptus grandis × Eucalyptus urophylla (G9), to Al toxicity, seedling roots were treated hydroponically with an Al solution, and the polysaccharide content in the root tip cell wall and the characteristics of programmed cell death were studied. The results show that the distribution of Al was similar in both clones, although G9 was found to be more tolerant to Al toxicity than G4. The Al3+ uptake of pectin in root tip cell walls was significantly higher in G4 than in G9. The root tip in G4 was obviously damaged, enlarged, thickened, and shorter; the root crown cells were cracked and fluffy; and the cell elongation area was squeezed. The lower cell wall polysaccharide content and PME activity may result in fewer carboxylic groups in the root tip cell wall to serve as Al-binding sites, which may explain the stronger Al resistance of G9 than G4. The uptake of nitrogen and potassium in G4 was significantly reduced after aluminum application and was lower than in G9. Al-resistant Eucalyptus clones may have synergistic pleiotropic effects in resisting high aluminum-low phosphorus stress, and maintaining higher nitrogen and potassium levels in roots may be an important mechanism for effectively alleviating Al toxicity.

[Distribution of phosphorus fractions in soil aggregates in Chinese fir plantations with different stand ages]. / ä¸åŒæž—é¾„æ‰æœ¨äººå·¥æž—åœŸå£¤å›¢èšä½“ç£·ç´ åˆ†å¸ƒç‰¹å¾.

Exploring the distribution of phosphorus (P) fractionsin soil aggregates is helpful to improve soil P availa-bility during Chinese fir planting. In this study, soil samples were collected in the 0-20 cm soil layer from Chinese fir plantations with different stand ages (9 a, 17 a, and 26 a) and one nearby abandoned land (CK) in Rongshui County, Guangxi, China. Soil aggregates were classified into >2 mm, 1-2 mm, 0.25-1 mm, and <0.25 mm size classes through dry-sieving process, and then soil P fractions in different sized aggregates were measured. These results showed that: 1) The composition of soil aggregates showed significant difference among different stand ages. As the major aggregate fractions in soil, the contents of >2 mm aggregates increased firstly and then decreased over time, and peaked in the 17 a Chinese fir plantation. The changes of soil mean weight diameter (MWD) and geometric mean diameter (GMD) during Chinese fir planting were the same as the content of >2 mm aggregates. 2) Soil total P, inorganic P, and organic P contents did not differ among different sized aggregates. However, soil available P content was mainly distributed in >2 mm aggregates with a range of 1.23-7.33 mg·kg-1. Compared with CK, soil total P, available P, and inorganic P contents were significantly higher in Chinese fir plantations, and their contents increased firstly and then decreased over time. Soil total P (322.40 mg·kg-1) and available P (7.33 mg·kg-1) contents were the highest in the 9 a plantations, and soil inorganic P content (114.05 mg·kg-1) was the highest in the 17 a plantation. Moreover, soil organic P content showed an order of 9 a > 26 a >17 a > CK, with the highest content (210.00 mg·kg-1) in the 9 a plantation. 3) The distribution of P stock in soil aggregates was related to the contents of different sized aggregates, with >2 mm aggregates having the highest P stock. Except for organic P, soil P stock increased firstly and then decreased with the increases of stand age. In conclusion, Chinese fir planting was helpful to improve soil aggregate stability and to promote the increase of soil P level before the stand age of 17 a. However, Chinese fir planting could result in the degradation of soil aggregates and in the decrease of soil P level after 17 a. The formation and stabilization of >2 mm aggregates played an important role in the maintenance of soil quality and soil P supply level after 17 a Chinese fir planting.

The physiological and molecular mechanisms of N transfer in Eucalyptus and Dalbergia odorifera intercropping systems using root proteomics.

BACKGROUND: The mixing of Eucalyptus with N2-fixing trees species (NFTs) is a frequently successful and sustainable cropping practice. In this study, we evaluated nitrogen (N) transfer and conducted a proteomic analysis of the seedlings of Eucalyptus urophylla × E. grandis (Eucalyptus) and an NFT, Dalbergia (D.) odorifera, from intercropping and monocropping systems to elucidate the physiological effects and molecular mechanisms of N transfer in mixed Eucalyptus and D. odorifera systems. RESULTS: N transfer occurred from D. odorifera to Eucalyptus at a rate of 14.61% in the intercropping system, which increased N uptake and growth in Eucalyptus but inhibited growth in D. odorifera. There were 285 and 288 differentially expressed proteins by greater than 1.5-fold in Eucalyptus and D. odorifera roots with intercropping vs monoculture, respectively. Introduction of D. odorifera increased the stress resistance ability of Eucalyptus, while D. odorifera stress resistance was increased by increasing levels of jasmonic acid (JA). Additionally, the differentially expressed proteins of N metabolism, such as glutamine synthetase nodule isozyme (GS), were upregulated to enhance N competition in Eucalyptus. Importantly, more proteins were involved in synthetic pathways than in metabolic pathways in Eucalyptus because of the benefit of N transfer, and the two groups of N compound transporters were found in Eucalyptus; however, more functional proteins were involved in metabolic degradation in D. odorifera; specifically, the molecular mechanism of the transfer of N from D. odorifera to Eucalyptus was explained by proteomics. CONCLUSIONS: Our study suggests that N transfer occurred from D. odorifera to Eucalyptus and was affected by the variations in the differentially expressed proteins. We anticipate that these results can be verified in field experiments for the sustainable development of Eucalyptus plantations.

The Abundance and Structure of Deadwood: A Comparison of Mixed and Thinned Chinese Fir Plantations.

The sustainability of coniferous monoculture plantations is facing challenges with respect to yields, ecology, and biodiversity. Conversion of monocultural coniferous plantations into mixed stands using thinning or direct mixed planting is widely considered to be a key strategy for overcoming these challenges and transforming the characteristics of plantations on a regional scale. Substantial amounts of deadwood may be produced in mixed forests (MFs); this material is important for evaluating and modifying forest management methods, understanding the dynamics of forest stands, and achieving biodiversity conservation. We assessed the quantitative characters and diameter distributions of deadwood in mixed and thinned Chinese fir [Cunninghamia lanceolata (Lamb.) Hook.] forests over one rotation. We used the g(r) function and spatial parameters to analyze the spatial structure of deadwood, and used logistic regression and Hegyi's competition index (HCI) to explore competition and mortality. Our results indicate that: (1) Chinese fir dominated in all groups of deadwood (snags, broken wood, and fallen wood), and the abundance, volume, and mortality rates of deadwood were much lower in the thinning forest compared to the MF. (2) Later coming populations (LCPs) comprised the majority of the small diameter classes in the thinning forest, but only accounted for a small proportion of the MF. (3) Broken wood in the thinning forest was randomly distributed, while the other types of deadwood were clustered at most spatial scales. In contrast, the spatial patterns in the MF were random at most spatial scales. (4) Total deadwood in both stands was in a status of intermediate and was randomly surrounded by its four nearest neighbors. All types of deadwood were highly mixed in the thinning forest and moderately mixed in the MF. Our case study suggests that thinning and mixing result in different stand development processes and thus influence the type, amount, and structure of deadwood. Thinning significantly reduces competition, which is the main driver of tree mortality. Converting pure Chinese fir plantations into mixed stands by thinning should be taken in future. Understanding tree mortality after conversion is essential to select appropriate silvicultural treatments and achieve ultimately sustainable forest management.

[Effects of Cunninghamia lanceolata stand types on the changes of aggregate-related organic carbon and nutrients in surface soil]. / æ‰æœ¨æž—åˆ†ç±»åž‹å¯¹è¡¨å±‚åœŸå£¤å›¢èšä½“æœ‰æœºç¢³åŠå »åˆ†å˜åŒ–çš„å½±å“.

Exploring the microscopic characterization of organic carbon and nutrients in surface soil of different Chinese fir stands at aggregate scale can lay a theoretical foundation for promoting the sustainable use of soil resources with implications for improving soil health and fertility. We mea-sured the concentrations of soil organic C (OC), total nitrogen (TN), alkali-hydrolyzed nitrogen (AN), Olsen-P (AP), and available K (AK) in aggregate fractions collected from 0-10 cm and 10-20 cm soil layers in three different stands, mixed plantation of Cunninghamia lanceolata and Michelia macclurei (Ⅰ), C. lanceolata and Mytilaria laosensis (Ⅱ) and pure plantation of C. lanceolata (Ⅲ) respectively. Soil aggregates were classified into >2, 0.25-2, and <0.25 mm fractions by a dry-sieving procedure. The organic carbon and nutrient contents of soil aggregates in different stands increased with the decreases of particle size while the contribution rate of aggregates with different particle sizes to soil organic carbon and nutrient storage in 0-10 cm soil layer mainly was (>2 mm)>(0.25-2 mm)>(<0.25 mm), which was (>2 mm)>(<0.25 mm)>(0.25-2 mm) in 10-20 cm soil layer. The average weight diameter (MWD), the contents and stocks of OC, TN, AN and AP in surface soil aggregates of different stands ranked as Ⅰ>Ⅱ>Ⅲ (except the AP in 10-20 cm soil layer), while the contents and stocks of AK ranked as Ⅲ>Ⅰ>Ⅱ. Compared with pure plantation, aggregate structure of surface soil of mixed plantations was more stable, and Ⅰ was better than Ⅱ, because Ⅰ was artificially disturbed but Ⅱwas not. Therefore, the mixed plantation of C. lanceolata and M. macclurei could effectively promote the formation and stability of soil aggregates, and alleviate decomposition of soil organic matter and nutrient loss in plantations.

[Responses of soil aggregate-associated organic carbon and nutrients to tea cultivation age in southern Guangxi, China]. / æ¡‚å—èŒ¶å›­åœŸå£¤å›¢èšä½“æœ‰æœºç¢³å’Œå »åˆ†å¯¹æ¤èŒ¶å¹´é™çš„å“åº”.

Understanding the response mechanism of soil aggregate-associated organic carbon (OC) and nutrients to tea cultivation age can lay a theoretical foundation for improving soil fertility, ensuring soil health, and promoting sustainable utilization of soil resources in the tea plantations. In this study, concentrations of soil OC and nutrient were analyzed in >2, 2-1, 1-0.25, and <0.25 mm fractions (split by a dry-sieving procedure) at the 0-20 cm soil layer in four tea plantations with Baimao tea of different ages (8, 17, 25, and 43 a) in southern Guangxi, China. The distribution of soil aggregates showed that the dominant aggregates were >2 mm fractions with a mean value of 63.8%, followed by <0.25 mm fractions, while 2-1 and 1-0.25 mm fractions with mean values of 9.9% and 7.8%, respectively. As an indicator of soil aggregate stability, the mean weight diameter (MWD) in the tea plantations showed an order of 17 a >8 a >25 a >43 a. Regardless of tea cultivation age, soil aggregate-associated OC and total nitrogen (TN) concentrations increased with increasing aggregate size. Soil OC and TN concentrations in >2 and 2-1 mm fractions were significantly higher than those in other fractions. The mean values of soil OC and TN concentrations were 18.76 and 0.84 g·kg-1 in the >2 mm fractions, and were 18.65 and 0.80 g·kg-1 in the 2-1 mm fraction. Soil aggregate-associated available nitrogen (AN), available phosphorus (AP), and availa-ble potassium (AK) concentrations were highest in the <0.25 mm fractions with mean values of 50.43, 23.06, and 68.04 mg·kg-1, respectively. Long-term tea cultivation was favorable to the accumulation of soil OC, TN, AN, and AP, whereas the accumulation rates of these element stocks in the whole soil decreased with increasing tea cultivation age. In contrast, soil AK was susceptible to leaching in tea cultivation, with the loss rate of this element stock in the middle stage (from 17 to 25 a) being higher than those in the other stages. To ensure soil quality and promote the sustainable utilization of soil resources, more attention should be paid to the problems such as the decrease of soil aggregate stability and the aggravation of AK loss after 17 a of tea cultivation.

Effect of Low pH and Aluminum Toxicity on the Photosynthetic Characteristics of Different Fast-Growing Eucalyptus Vegetatively Propagated Clones.

Knowing how acid soils and aluminum in soils may limit the growth of Eucalyptus trees in plantations is important because these plantations grow in many tropical and subtropical regions. Seedlings of four vegetatively propagated Eucalyptus clones, E. grandis × E. urophylla 'GLGU9'(G9), E. grandis × E. urophylla 'GLGU12' (G12), E. urophylla × E. camaldulensis 'GLUC3' (G3) and E. urophylla 'GLU4'(G4), were subjected to liquid culture with Hoagland nutrient solution for 40 days, then treated with four different treatments of acid and aluminum for 1 day. The four treatments used either pH 3.0 or 4.0 with or without added aluminum (4.4 mM) in all possible combinations; a control used no added aluminum at pH 4.8. Subsequently, the photosynthetic parameters and morphology of leaves from eucalypt seedlings were determined and observed. The results showed that the tested chlorophyll content, net photosynthetic rate, transpiration rate and water use efficiency were apparently inhibited by aluminum. Under uniform Al concentration (4.4 mM), the Al-induced limitation to photosynthetic parameters increased with pH, indicating acid stimulation to Al toxicity. Among all treatments, the most significant reduction was found in the combination of pH 3.0 and 4.4 mM Al. The photosynthetic and transpiration rates showed similar trends with G9 > G12 > G3 > G4, suggesting that G9 and G12 had higher Al-tolerance than other two clones. Microscopic observation revealed changes in leaf morphology when exposed to Al stress; for example, a reduced thickness of leaf epidermis and palisade tissue, the descendant palisade tissue/spongy tissue ratio and leaf tissue looseness. Overall, the acid and aluminum stress exerted negative effects on the photosynthetic activity of eucalypt seedlings, but the differences in tolerance to Al toxicity between the clones were favorable, offering potential to improve Eucalyptus plantation productivity by selecting Al tolerant clones.