Respiration rate of moss-dominated biocrusts and their relationships with temperature and moisture in a semiarid ecosystem

Abstract

Biocrusts are widely distributed throughout the world in dryland ecosystems, but their respiration rate (Rs) and responses to soil temperature and mositure have not yet been fully investigated. In a semiarid region of the Loess Plateau in China, the Rs of moss-dominated biocrusts was continuously (104 days) measured in summer through an automated soil respiration system, and their relationships with soil temperature and moisture at 2, 5, and 10 cm depths were intensively analyzed. The results showed the biocrusts had 115% higher (t = −3.82, P < 0.001) Rs during day and 44% higher (t = −10.22, P < 0.001) Rs during night as compared with the underlying soil; they averagely increased Rs by 81% (2.52 vs. 1.39 μmol m−2 s−1) across day and night. More specifically, the Rs of biocrusts ranged from 0.33 to 6.33 μmol m−2 s−1 in wet conditions (soil moisture ≥ 0.15 cm3 cm−3) and 0.27 to 2.83 μmol m−2 s−1 in dry conditions (soil moisture = 0.05 cm3 cm−3), with a daily mean of 2.11 μmol m−2 s−1. Particularly, in wet conditions the Rs of biocrusts had positive responses to increasing temperature, and their relationship was well fitted with an exponential function (R2 ≥ 0.44; P < 0.001), with a Q10 value ranging between 1.73 and 2.08. Similarly, the Rs of biocrusts was positively correlated with soil moisture, but their relationship was not well fitted with the quadratic function (R2 ≤ 0.22). A model based on the soil moisture and temperature at 2 cm depth performed much better (R2 = 0.53; P < 0.001) with Rs than that based on the soil moisture and temperature at 5 or 10 cm depth or even air temperature. In conclusion, moss biocrusts made a significant contribution to soil respiration in semiarid ecosystem, firstly (and directly) due to the rich and diversified microbial communities in biocrust layer and secondly (and indirectly) due to the biocrust effects on soil temperature and moisture regimes. The temperature and moisture at 2 cm depth (biocrust layer) should be employed with a higher priority in simulating Rs of biocrusted surfaces, rather than the commonly used soil depth (5 cm) in estimating Rs of the ordinary soil without biocrusts.