蒋家沟干热河谷区灌草层植被与土壤的养分分布及生态化学计量特征

Nutrient Distribution and Ecological Stoichiometry Characteristics of Shrub-Grass Layer Vegetation and Soil in the Jiangjia Gully,China

蒋家沟干热河谷区泥石流与滑坡灾害频发、植被枯败稀疏、土壤结构紊乱、生态环境脆弱,是金沙江上游生态严重退化的典型流域。植被和土壤在退化生态系统修复和治理中扮演着至关重要的角色。对该流域植被与土壤的研究,多侧重从单一物种或土壤酶活性等角度分析植被与土壤的养分耦合关系,缺少对灌草层植物体养分含量与土壤养分含量的耦合机制研究,即植被-土壤耦合机制机理尚不明确。本文选取蒋家沟干热河谷区典型灌草层植被,研究碳(C)、氮(N)、磷(P)、钾(K)元素在植被地上、根系和土壤的养分分布和生态化学计量特征及其相关性。结果显示:(1)与全国陆地植物平均水平相比,干热河谷区灌草层植被地上和根系表现出低C,高N、P、K的特点;土壤表现出低C高P的特点。(2)植被地上部分的C、N、P、K含量均显著高于根系,C、N、P含量均显著高于土壤;土壤K含量(56.05 g/kg)显著高于植被地上(18.43 g/kg)和根系(8.41 g/kg);除P:K外(地上0.10>根系0.09>土壤0.01),其余5种化学计量比均表现为根系>地上>土壤。(3)灌草层植被地上、根系N、P、K含量及生态化学计量特征间均呈正相关,土壤与植被的C、N、P、K含量和化学计量比多数不存在相关性。(4)植被地上部分C:N(21.07)、C:P(247.05)、N:P(12.32)均低于根系(分别为32.95、512.10和15.71),符合“生长速率假说”。根据N:P、N:K、P:K判断,灌草层植被生长不受P、K限制而更易受到N的限制。根据C:N、C:P、N:P判断,与全国表层土壤平均值相比,土壤贫瘠缺乏C、N元素,P有效性较低。(5)植被地上和根系在养分的分配过程中具有协同性。干热河谷区气候条件下植物应对策略为选择提高生长速率、降低养分利用效率。蒋家沟流域生态恢复应增加土壤有机碳和氮素的含量来改善土壤环境,降低N元素对植物的限制。本研究可为改善蒋家沟流域生态环境提供参考。

The dry-hot valley of the Jiangjia Gully in the upper reaches of the Jinsha River is a typical basin with severe ecological degradation,which urgently needs restoration and management because of the frequent occurrence of mudslides and landslides,sparse vegetation,soil structure disorganization,and fragile ecological environment.Vegetation and soil play a crucial role in the restoration and management of degraded ecosystems.Previous research on vegetation and soil in this basin focused on analyzing the coupling relationship between vegetation and soil from a perspective of a single species or soil enzyme activity.However,there was a lack of research on the coupling mechanism between vegetation and soil nutrient content in the scrub layer,and the vegetation-soil coupling mechanism was not yet clear.In this study,typical shrub-stratum vegetation in the dry-hot river valley areas of the Jiangjia Gully was collected as research object.It investigated nutrient distribution and ecological stoichiometric characteristics of carbon(C),nitrogen(N),phosphorus(P)and potassium(K)in the aboveground vegetation,root systems,and soil,as well as their correlation.It found that(1)compared with national average of terrestrial plants,the aboveground and root systems of the shrub-grass layer in dry-hot river valley area were characterized by low carbon,high nitrogen,phosphorus and potassium,whereas the soil was low in carbon and high in phosphorus.(2)The C,N,P and K contents of aboveground vegetation parts were significantly higher than those of the root system and the contents of C,N and P in the aboveground vegetation were significantly higher than those in the soil.K content in the soil(56.05 g·kg-1)was significantly higher than that in the aboveground vegetation(18.43 g·kg-1)and the root system(8.41 g·kg-1).With the exception of P:K(aboveground 0.10>root system 0.09>soil 0.01),the remaining five stoichiometric ratios showed the following order:root system>aboveground>soil.(3)Positive correlations were found between aboveground and root system N,P,and K contents and the ecological stoichiometric characteristics of vegetation in the scrub layer,whereas most C,N,P,and K contents and stoichiometric ratios of soil and vegetation were not correlated.(4)The aboveground C:N(21.07),C:P(247.05),and N:P(12.32)ratios of vegetation were lower than those of the root system(32.95,512.10 and 15.71,respectively),which was consistent with the“growth rate hypothesis”.According to the N:P,N:K and P:K ratios,the growth of the shrub and grass layer vegetation was not limited by P and K,but was more vulnerable to N limitation.Comparison of the C:N,C:P and N:P ratios with the national average of surface soil,showed that the soil was barren and lacked C and N while P availability was low.(5)Aboveground vegetation and root systems acted synergistically in the process of nutrient allocation.In summary,the plant coping strategy under climatic conditions of dry and hot river valley area is to increase the growth rate and reduce nutrient utilization efficiency.Ecological restoration of the Jiangjia Gully watershed should focus on soil organic carbon and nitrogen content and reduce the limitation of N to plants.This study can provide a reference for improving the ecological environment of the Jiangjia Gully watershed.