氮磷添加下黄土丘陵区退耕草地土壤呼吸速率日变化特征

Effects of nitrogen and phosphorus addition on diurnal variations of soil respiration rate in the grassland and farm withdrawing cultivation on Loess Hilly-gully Region

为探究黄土丘陵区退耕草地土壤呼吸及其组分日变化对氮磷添加的响应,采用裂区试验设计,主区施氮[0,50和100kg N/(hm^(2)·a)]和副区施磷[0,40和80kg P_(2)O_(5)/(hm^(2)·a)],于2019年5~8月每月测定各处理下土壤呼吸速率、异养呼吸速率及土壤温度和含水量日变化.结果表明,土壤呼吸速率及其组分日变化均呈单峰曲线,峰值出现在12:00~14:00.与不施肥相比,土壤呼吸、异养呼吸和自养呼吸速率在单施氮下分别增加7.31%~13.13%,1.12%~12.43%和7.64%~46.26%,单施磷下分别增加16.84%~18.42%,11.48%~14.22%和17.15%~29.59%,氮磷配施下分别增加24.17%~27.30%,21.94%~32.43%和34.05%~41.26%.不同氮磷添加下土壤呼吸、异养呼吸和自养呼吸碳排放量昼占比分别为52.68%~61.37%,50.92%~58.70%和51.39%~76.35%.50kg N/(hm^(2)·a)和80kg P_(2)O_(5)/(hm^(2)·a)配施处理的土壤累积CO_(2)排放量(2012g/m^(2))最高,不施肥处理的土壤累积CO_(2)排放量(1531g/m^(2))最低.各处理的土壤呼吸,异养呼吸和自养呼吸均与土壤温度呈显著指数正相关关系,其温度敏感性(Q_(10))变化范围分别为1.19~1.86,1.08~1.81和1.11~3.67,氮磷添加降低异养呼吸的Q_(10)值,但提高自养呼吸的Q_(10)值.总体表明,氮磷添加增加土壤呼吸及其组分速率,降低异养呼吸的温度敏感性,氮磷添加对土壤呼吸及其组分速率的促进效果与氮磷添加量及其配比有关.

In order to explore the response characteristics of soil respiration(Rs)and its components(heterotrophic respiration,Rh;and autotrophic respiration,Ra)to N and P additions in the grassland and farm withdrawing cultivation,a field split-plot experiment was performed including:[main-plots with 0,50,and 100kg N/(hm^(2)·a)];and[subplots:with 0,40 and 80kg P_(2)O_(5)/(hm^(2)·a)].Such treatments were made every month from May to August in 2019 and for each treatment,these treatments were made:diurnal variations of Rs and Rh and Ra,soil temperature(Ts)and soil water content.Results showed that the diurnal variations of Rs and its two components(i.e.Rh and Ra)showed single-peak curves across all N and P addition treatments,and all reached the maximum values between 12:00~14:00.Compared with no fertilization treatment(CK),Rs,Rh and Ra increased significantly under N addition by 7.31%~13.13%,1.12%~12.43%and 7.64%~46.26%,respectively,and increased significantly under P addition by 16.84%~18.42%,11.48%~14.22%and 17.15%~29.59%respectively.N and P combined addition increased Rs,Rh and Ra by 24.17%~27.30%,21.94%~32.43%and 34.05%~41.26%,respectively.The daytime proportions of whole day carbon emissions from Rs,Rh and Ra under different N and P addition treatments accounted for 52.68%~61.37%,50.92%~58.70%and 51.39%~76.35%,respectively.The cumulative CO_(2)emission was the highest at 2012g/m^(2) under a treatment of 50kg N/(hm^(2)·a)combined with 80kg P_(2)O_(5)/(hm^(2)·a),and the lowest appeared under no fertilization treatment at 1531g/m^(2).Rs and its two components(Rh and Ra)were significantly positively correlated with the soil temperature(Ts),and their temperature sensitivity(Q_(10))ranged from 1.19 to 1.86,1.08 to 1.81,and 1.11 to 3.67,respectively.N and P decreased the Q_(10) values of Rh,but increased the Q_(10) values of Ra.In summary,N and P additions increase the rates of Rs and its two components,but decreased the temperature sensitivity of Rh,and the effect of N and P addition on soil respiration rate were related to N and P addition amounts and their ratios.