高寒草甸植物叶片氮和磷重吸收率对养分添加的响应及机理

【目的】本研究旨在揭示植物叶片氮和磷重吸收率对氮磷添加及交互作用的响应和机理,明确高寒草甸植物养分利用策略多样性。【方法】以高寒草甸优势植物(垂穗披碱草、发草、灰苞蒿和鹅绒委陵菜)为研究对象,基于氮和磷添加两因子交互试验,研究高寒植物叶片养分重吸收率对养分添加的响应。【结果】(1)禾本科叶片氮重吸收率随氮添加而增加,但杂类草叶片不受影响;此外,4种植物叶片磷重吸收率均不受氮添加的影响。(2)磷添加对所有植物叶片氮重吸收率和两种杂类草叶片磷重吸收率没有显著影响,但提高了禾本科叶片的磷重吸收率。(3)氮和磷共同添加降低了垂穗披碱草、灰苞蒿和鹅绒委陵菜叶片氮重吸收率,但提高了发草叶片的氮重吸收率。此外,氮和磷同时添加对4种植物叶片磷重吸收效率没有显著影响。【结论】综上所述,本研究揭示了养分富集下高寒植物3种不同的养分重吸收策略,即对外源获取的养分全部重吸收(绿叶养分增加但凋落叶不增加)、部分重吸收(绿叶和凋落叶同时增加,但凋落叶增加较慢)和不进行重吸收(绿叶和凋落叶均增加,但凋落叶的幅度大于或等于绿叶;或绿叶和凋落叶不响应)。这些研究结果为理解高寒植物养分内循环策略的多样性和互补性提供了一定的启示。

Experimental evidence for weakened tree nutrient use and resorption efficiencies under severe drought in a subtropical monsoon forest

Aims The functions of global forests are threatened by the increasing frequency of severe drought.Due to drought inducing reductions in soil nutrient availability,efficiencies of nutrient use and resorption of trees become crucial for forest functions and biogeochemical cycles.However,understanding the dynamics of responses of foliar nutrient use and resorption efficiencies to drought,especially in tropical or subtropical forests,is still limited.Our goal was to detect whether and how the importance of leaf nutrient use and resorption changes across different species in the hot and wet forests when suffering drought stress in different months.Methods Based on a 70%throughfall exclusion experiment in a subtropical forest,we collected green and senesced leaves of Schima superba and Lithocarpus glaber in different months from October 2016 to May 2019,to estimate the effects of drought on leaf nitrogen(N)and phosphorus(P)use and resorption efficiencies(i.e.NUE and PUE,NRE and PRE).Important Findings The effects of drought on nutrient use and resorption efficiencies varied between species and months.Based on a 2-year observation,drought had no effect on S.superba,but significantly decreased NUE,NRE and PRE of L.glaber by 3.4%,20.2%and 7.1%,respectively.Furthermore,the negative drought effects were aggravated by the natural summer drying in 2017.As a result,NUE and PUE of L.glaber were significantly depressed by 17.2%and 58.1%,while NRE and PRE were significantly reduced by 56.5%and 53.8%in August 2017.Moreover,the responses of NRE,PRE and NUE to drought were related with soil moisture(SM)for L.glaber,and when SM decreased to a threshold near 9 v/v%,drought effects were shifted from unresponsive to negative.Our results highlight a species-specific threshold response of nutrient use under drought in a subtropical forest.

N limitation increases along a temperate forest succession:evidences from leaf stoichiometry and nutrient resorption

Forest productivity and carbon(C) sequestration largely depend on soil N and P availability.To date,however,the temporal variation of nutrient limitation along forest succession is still under debate.Leaf stoichiometry and nutrient resorption are important indicators for predicting nutrient limitation of plant growth.Here,we measured nitrogen(N)and phosphorus(P)concentrations in green leaves and leaf liter for all woody species at four stages of temperate forest succession,and analyzed how abiotic and biotic factors affect leaf stoichiometry and nutrient resorption along forest succession.At the individual scale,leaf N and P concentrations had a significant increase at the end of the succession,while no change in leaf N:P ratio was detected.Nitrogen resorption efficiency(NRE)increased significantly with succession,but P resorption efficiency(PRE)first increased and then decreased.Significant increases in NRE:PRE ratios only occurred at the end of the succession.Moreover,plant N cycling was less responsive to soil nutrient than P cycling.At the community scale,we found that leaf N and P concentrations first decreased and then increased along forest succession,which were mainly affected by Shannon-Wiener index and species richness.Leaf N:P ratio significantly varied with succession and was mainly determined by community-weighted mean diameter at breast height(DBH).NRE increased and was significantly influenced by species richness and DBH,while PRE was relatively stable along forest succession.Thus,the NRE:PRE ratios significantly increased,indicating that N limitation is exacerbated with the temperate forest succession.These results might reflect the intense interspecific competition for limiting resource in a higher biodiversity community.In conclusion,our findings highlight the importance of biotic factors in driving forest ecosystem nutrient cycling and provide valuable information for sustainable fertilizer management practices in China's temperate and boreal forests.