Impacts of Defoliation on Morphological Characteristics and Non-Structural Carbohydrates of Populus talassica × Populus euphratica Seedlings

Leaves are important‘source’organs that synthesize organic matter,providing carbon sources for plant growth.Here,we used Populus talassica×Populus euphratica,the dominant species in ecological and timber forests,to simulate carbon limitation through artificial 25%,50%,and 75%defoliation treatments and explore the effects on root,stem,and leaf morphology,biomass accumulation,and carbon allocation strategies.At the 60th d after treat-ment,under 25%defoliation treatment,the plant height,specific leaf weight,root surface area and volume,and concentrations of non-structural carbohydrates in stem and root were significantly increased by 9.13%,20.00%,16.60%,31.95%,5.12%,and 9.34%,respectively,relative to the control.There was no significant change in the growth indicators under 50%defoliation treatment,but the concentrations of non-structural carbohydrates in the leaf and stem significantly decreased,showing mostly a negative correlation between them.The opposite was observed in the root.Under 75%defoliation treatment,the plant height,ground diameter,leaf number,single leaf area,root,stem,and total biomass were significantly reduced by 14.15%,10.24%,14.86%,11.31%,11.56%,21.87%,and 16.82%,respectively,relative to the control.The concentrations of non-structural carbohydrates in various organs were significantly reduced,particularly in the consumption of the starch concentrations in the stem and root.These results indicated that carbon allocation strategies can be adjusted to increase the con-centration of non-structural carbohydrates in root and meet plant growth needs under 25%and 50%defoliation.However,75%defoliation significantly limited the distribution of non-structural carbohydrates to roots and stems,reduced carbon storage,and thus inhibited plant growth.Defoliation-induced carbon limitation altered the carbon allocation pattern of P.talassica×P.euphratica,and the relationship between carbon reserves in roots and tree growth recovery after defoliation was greater.This study provides a theoretical basis for the comprehen-sive management of P.talassica×P.euphratica plantations,as well as a reference for the study of plantation car-bon allocation strategies in the desert and semi-desert regions of Xinjiang under carbon-limitation conditions.

Effects of soil nitrate:ammonium ratio on plant carbon:nitrogen ratio and growth rate of Artemisia sphaerocephala seedlings

Can soil nitrate： ammonium ratios influence plant carbon： nitrogen ratios of the early succession plant？ Can plant carbon： nitrogen ratios limit the plant growth in early succession？ To address these two questions, we performed a two-factor （soil nitrate： ammonium ratio and plant density） randomized block design and a uniform-precision rotatable central composite design pot experiments to examine the relationships between soil nitrate： ammonium ratios, the carbon： nitrogen ratios and growth rate of Artemisia sphaerocephala seedlings. Under adequate nutrient status, both soil nitrate： ammonium ratios and plant density influenced the carbon： nitrogen ratios and growth rate of A. sphaerocephala seedlings. Under the lower soil nitrate： ammonium ratios, with the increase of soil nitrate： ammonium ratios, the growth rates of plant height and shoot biomass of A. sphaerocephala seedlings decreased significantly; with the increase of plant carbon： nitrogen ratios, the growth rates of shoot biomass of A. sphaerocephala seedlings decreased significantly. Soil nitrate： ammonium ratios affected the carbon： nitrogen ratios of A. sphaerocephala seedlings by plant nitrogen but not by plant carbon. Thus, soil nitrate： ammonium ratios influenced the carbon： nitrogen ratios of A. sphaerocephala seedlings, and hence influenced its growth rates. Our results suggest that under adequate nutrient environment, soil nitrate： ammonium ratios can be a limiting factor for the growth of the early succession plant.

Divergent allocations of nonstructural carbohydrates shape growth response to rainfall reduction in two subtropical plantations

Nonstructural carbohydrates(NSC)are indicators of tree carbon balance and play an important role in regulating plant growth and survival.However,our understanding of the mechanism underlying drought-induced response of NSC reserves remains limited.Here,we conducted a long-term throughfall exclusion(TFE)experiment to investigate the seasonal responses of NSC reserves to manipulative drought in two contrasting tree species(a broadleaved tree Castanopsis hystrix Miq.and a coniferous tree Pinus massoniana Lamb.)of the subtropical China.We found that in the dry season,the two tree species differed in their responses of NSC reserves to TFE at either the whole-tree level or by organs,with significantly depleted total NSC reserves in roots in both species.Under the TFE treatment,there were significant increases in the NSC pools of leaves and branches in C.hystrix,which were accompanied by significant decreases in fine root biomass and radial growth without significant changes in canopy photosynthesis;while P.massoniana exhibited significant increase in fine root biomass without significant changes in radial growth.Our results suggested that under prolonged water limitation,NSC usage for growth in C.hystrix is somewhat impaired,such that the TFE treatment resulted in NSC accumulation in aboveground organs(leaf and branch);whereas P.massoniana is capable of efficiently utilizing NSC reserves to maintain its growth under drought conditions.Our findings revealed divergent NSC allocations under experimental drought between the two contrasting tree species,which are important for better understanding the differential impacts of climate change on varying forest trees and plantation types in subtropical China.

Accumulation contribution differences between lacustrine organic-rich shales and mudstones and their significance in shale oil evaluation

The differences in organic matter abundance and rock composition between shale and mudstone determine the discrepancy of their contributions to the formation of conventional and shale oil/gas reservoirs.The evaluation criteria of source rocks are different in the future exploration in self-sourced petroleum systems.Shales are deposited in deep/semi-deep lacustrine,with low sedimentation rate and chemical depositions of various degrees,while mudstones are mostly formed in shallow lacustrine/lakeside,with high deposition rate and density flow characteristics.Three factors contribute to the enrichment of organic matter in shales,including the"fertility effect"caused by volcanic ash deposition and hydrothermal injection,excessive and over-speed growth of organisms promoted by radioactive materials,and deep-water anaerobic environment and low sedimentation rate to protect the accumulation of organic matter from dilution.Lamellations in shales are easy to be stripped into storage space,and acid water produced during hydrocarbon generation can dissolve some particles to generate new pores.The massive mudstones with high clay content are of poor matrix porosity.Shales with high total organic carbon,developed laminations,relatively good reservoir property,and high brittle mineral content,are the most favorable lithofacies for shale oil exploration and development.It is necessary to conduct investigation on the differences between shale and mudstone reservoirs,to identify resources distribution in shale and mudstone formations,determine the type and standard of"sweet-spot"evaluation parameters,optimize"sweet-spot areas/sections",and adopt effective development technologies,which is of great significance to objectively evaluate the total amount and economy of shale oil resources,as well as the scale of effective exploitation.