喀斯特不同植被恢复阶段土壤有机酸季节变化与有效氮磷的关系

植物分泌有机酸在提高土壤养分有效性方面起到重要作用。为了解喀斯特地区不同植被恢复阶段土壤有机酸含量季节性变化与氮磷有效性的关系,在灌木林和原生林各选择3种优势植物,测定雨季和旱季两个季节根际土和非根际土的有机酸含量、碳氮磷含量和比值、有效性氮磷含量及微生物生物量碳。结果表明:原生林植物根际土的草酸含量高于灌木林,而苹果酸和乙酸含量则低于灌木林;根际土草酸含量均高于非根际土;2个植被根际土和非根际土的草酸含量在雨季高于旱季,而苹果酸和乙酸含量则低于旱季;土壤草酸含量与有机碳、全氮、全磷和N∶P值呈显著正相关,与C∶N呈显著负相关;土壤有效氮和有效磷与草酸和微生物生物量碳呈显著正相关。上述结果表明,植物分泌有机酸的季节性变化与土壤养分状态和自身养分需求相关,而有机酸耦合微生物对养分有效性的提高具有积极的作用。因此,根际土的有机酸季节变化可能是喀斯特生态系统中植物适应土壤养分限制的一种重要机制。

Seasonal changes of soil organic acid concentrations in relation to available N and P at different stages of vegetation restoration in a karst ecosystem.

Soil organic acids released by plants are important for improving soil nutrient availability.To clarify the relationships between soil organic acids and the concentrations and ratios of nutrients at different stages of vegetation restoration in a karst ecosystem,we measured the concentrations of oxalic acid,malic acid,acetic acid,organic carbon(SOC),total nitrogen(TN),total phosphorus(TP),nitrogen(AN)and phosphorus availability(AP),and microbial biomass carbon(MBC)in rhizosphere soils and bulk soils of six plant species(three for shrubland and three for primary forest)in dry and wet seasons.Our results showed that the oxalic acid concentrations of rhizosphere soils in primary forest were higher than those in shrubland in both seasons,whereas the concentrations of malic acid and acetic acid showed an opposite trend.Moreover,the concentrations of oxalic acid in rhizosphere soils in both vegetations were higher than those of bulk soils in both seasons.The concentrations of oxalic acid of rhizosphere and bulk soils were higher in the wet season than that in the dry season,whereas those of malic acid and acetic acid were lower.Furthermore,the oxalic acid concentrations were significantly positively correlated with SOC,TN,TP,AN,and N∶P ratios,and significantly negatively correlated with C∶N ratios.Soil AN and AP concentrations were significantly positively correlated with oxalic acid concentrations and MBC.Our results suggest that seasonal changes in organic acid exudate may be related to soil nutrient status and plant nutrition requirements,and that the interactions between organic acids and soil microorganisms may enhance nitrogen and phosphorus availability.Therefore,seasonal changes in organic acid concentrations of rhizosphere soils may be an important mechanism for plant adaption to soil nutrient limitations in karst ecosystems.