冻融变化对西南亚高山森林优势种云杉和华西箭竹根区土壤理化性质与酶活性的影响

Effects of freeze-thaw changes on soil physicochemical properties and enzyme activities in root zone of Picea asperata and Fargesia nitida under subalpine forests of southwest China

西南亚高山森林是典型的季节性冻土区,为深入研究气候变暖背景下冻融循环变化对森林土壤环境的影响,该研究以西南亚高山森林乔木层与灌木层优势种云杉(Picea asperata)和华西箭竹(Fargesia nitida)根区土壤为研究对象,利用红外辐射加热器模拟气候变暖,研究增温对非生长季土壤冻融循环、土壤理化性质和酶活性的影响。在此基础上,开展室内培养实验,进一步验证冻融循环变化对土壤性质的影响。结果表明:(1)与对照小区比较,增温小区5cm和15cm土层温度分别升高2.85和2.13℃,冻结天数分别减少了60和32天,冻融循环次数分别由3次和1次降为0次。(2)增温增加了两物种根区土壤总氮(TN)、可溶性有机氮(DON)和微生物生物量氮(MBN)含量,但降低了土壤铵态氮(NH_(4)^(+)-N)含量。土壤冻结天数、冻融循环次数与TN、DON含量显著负相关,与NH_(4)^(+)-N含量显著正相关。(3)增温显著促进了两树种根区土壤N-乙酰-β-D-葡萄糖苷酶(NAG)活性,但显著抑制了脲酶(Ure)活性。土壤冻结天数、冻融次数与NAG和Ure活性显著相关。(4)与野外研究相似,室内冻融循环处理可显著增加云杉根区土壤NH_(4)^(+)-N含量与β-葡萄糖苷酶(BG)活性,降低了NAG活性;增加了华西箭竹根区NH_(4)^(+)-N含量,降低了BG与NAG酶活性;但冻融循环对土壤硝态氮(NO_(3)^(-)-N)、DON含量、Ure及蛋白酶(Pro)活性的影响与野外研究结果不同。冗余分析表明,华西箭竹根区土壤酶活性主要受土壤DON含量的影响,而云杉根区土壤酶活性与pH、NH_(4)^(+)-N含量、DON含量显著相关。以上结果说明,气候变暖背景下季节性冻土冻融循环消失,会显著影响西南亚高山森林非生长季土壤理化性质(尤其是土壤氮库组分)和酶活性,但其影响机制需要进一步研究。

Aims The subalpine forests of southwest China belongs to a typical seasonal frozen soil area.This study aimed to explore the effects of freeze-thaw changes on the soil physicochemical properties and enzyme activities under forest soils in response to climate warming.Methods Infrared radiation heaters were applied to simulate climate warming.Soils in the root zone of Picea asperata and Fargesia nitida were collected to explore the effects of warming on soil freeze-thaw cycles,soil physicochemical properties and enzyme activities.Meanwhile,soil incubation experiments were conducted to further analyze the effects of different freeze-thaw cycles on soil properties.Important findings Our results showed that(1)Experimental warming increased the soil temperatures by 2.85 and 2.13℃,decreased freezing days by 60 and 32 days,and also declined freeze-thaw cycles from 1-3 times to 0 time at the 5 cm and 15 cm soil depths,respectively.(2)Warming increased the contents of soil total nitrogen(TN),dissolved organic nitrogen(DON)and microbial biomass nitrogen(MBN),but significantly reduced the content of ammonium nitrogen(NH_(4)^(+)-N)under both P.asperata and F.nitida plots.The soil freezing days and number of freeze-thaw cycles were significantly negatively correlated with TN and DON contents,and significantly positively correlated with NH_(4)^(+)-N content.(3)Warming significantly promoted the activity ofβ-N-acetylglucosaminidase(NAG),but significantly inhibited the activity of urease(Ure)under the root zone soil of the two species.The activities of NAG and Ure were significantly correlated with freezing days and the number of freeze-thaw cycles.(4)Similar to results of the field study,the simulated freeze-thaw cycles significantly increased NH_(4)^(+)-N content and 4-methylumbelliferyl-β-D-glucoside(BG)activity,but decreased NAG activity under the root zone soil of P.asperata.On the other hand,freeze-thaw cycles increased NH_(4)^(+)-N content and reduced the activities of NAG and BG under the root zone soil of F.nitida.However,the effects of freeze-thaw cycles on the contents of nitrate nitrogen(NO_(3)^(-)-N)and DON as well as the activities of Ure and protease(Pro)were different based on the results of field experiment.Redundancy analysis showed that soil enzyme activities under the root zone of F.nitida were mainly affected by DON content,whereas those parameters under the root zone of P.asperatawere significantly correlated with pH,NH_(4)^(+)-N and DON contents.These results suggested that the disappearance of freeze-thaw cycles caused by future climate warming would significantly affect the soil physicochemical properties(especially soil nitrogen pool)and enzyme activities during non-growing season under subalpine forests of southwest China.But the underlying mechanism needs further study.