短期氮添加对罗浮栲林根际和非根际土壤生物有效磷的影响

Effects of short-term nitrogen addition on bioavailable phosphorus in rhizosphere and bulk soils of a Castanopsis fabri forest

氮沉降通常会加剧土壤磷限制,微生物和植物将采取策略抵消这种负面影响。然而,氮添加下土壤微生物和/或植物如何影响土壤生物有效磷尚不明确。基于野外氮添加实验,测定了生长季(4月)和非生长季(10月)罗浮栲林根际和非根际土壤理化性质,微生物生物量,磷酸酶活性以及根系形态和养分,并通过生物学方法量化了四种形式的生物有效磷,包括氯化钙-磷(CaCl_(2)-P),柠檬酸-磷(CA-P),盐酸-磷(HCl-P)和酶-磷(Enz-P)。研究结果表明,非生长季大多数生物有效磷表现为根际含量高于非根际,而生长季根际土壤CaCl_(2)-P和CA-P含量显著低于非根际土壤。氮添加显著增加了生长季非根际土壤CA-P含量,同时显著降低了非生长季根际土壤CaCl_(2)-P和Enz-P含量和显著增加了非生长季根际土壤HCl-P含量,但两个季节的总生物有效磷含量均保持不变。两个季节中,氮添加下植物细根比根长、比表面积和组织密度均存在不同程度的降低,但菌根侵染率显著增加,这说明氮添加下植物倾向于通过与菌根真菌合作而非改变根系形态来截留土壤中可直接获取的有效磷。从非生长季生物有效磷含量的动态来看,氮添加下植物根系和/或微生物通过释放质子活化矿质结合态无机磷对维持罗浮栲林土壤生物磷至关重要。总之,短期氮添加下维持了土壤有效磷的潜在供应。研究有助于进一步理解微生物和植物对低磷亚热带地区氮负荷的适应机制,可为制定缓解土壤磷限制的可持续策略提供理论依据。

Nitrogen deposition usually exacerbates soil phosphorus limitation,and microorganisms and plants will adopt strategies to offset this negative impact.However,it is unclear how soil microorganisms and/or plants affect soil bioavailable phosphorus under nitrogen addition.Based on field nitrogen addition experiments,this study determined physicochemical properties,microbial biomass and phosphatase activities of rhizosphere and bulk soils,and root morphology and nutrients during growing season(April)and non-growing season(October)in Castanopsis fabri forest.We quantified four forms of bioavailable phosphorus through biological methods,including calcium chloride phosphorus(CaCl_(2)-P),citric acid phosphorus(CA-P),hydrochloric acid phosphorus(HCl-P),and enzyme phosphorus(Enz-P).The results showed that contents of most bioavailable phosphorus in rhizosphere soils were higher than those in bulk soils during growing season,and contents of CaCl_(2)-P and CA-P in rhizosphere soils were significantly lower than those in bulk soils during non-growing season.Nitrogen addition significantly increased CA-P contents in bulk soils during growing season,while significantly reducing CaCl_(2)-P and Enz-P contents and significantly increasing HCl-P content in rhizosphere soils during non-growing season.However,the total bioavailable phosphorus content remained unchanged under nitrogen addition in the two seasons.In the two seasons,nitrogen addition resulted in varying degrees of reduction in root length,specific surface area,and tissue density of plant fine roots.However,a significant increase in mycorrhizal infection rate was observed,indicating that plants tended to intercept soil available phosphorus through cooperation with mycorrhizal fungi rather than changing root morphology under nitrogen addition.Additionally,no significant change in soil microbial biomass and phosphatase activity was found under nitrogen addition.From dynamics of bioavailable phosphorus content in non-growing season,it can be seen that plant roots and/or microorganisms activate mineral bound inorganic phosphorus by releasing protons under nitrogen addition,which is crucial for maintaining soil bioavailable phosphorus in Castanopsis fabri forest.It is worth noting that a higher response of bioavailable phosphorus to nitrogen addition was found in rhizosphere soil.Therefore,focusing solely on the dynamics of phosphorus availability in bulk soil may underestimate the impact of nitrogen addition on soil phosphorus availability.Overall,the short-term nitrogen addition maintained the potential supply of soil available phosphorus.This study helps to further understand adaptation mechanisms of microorganisms and plants to nitrogen load in low phosphorus subtropical regions,and provides a theoretical basis for the development of sustainable strategies to alleviate soil phosphorus limitation.