## Materials and Methods
### Flux Measurements  
Two weeks before the observations, a square metal base rim (50 cm \(\times\) 50 cm in area, 10 cm in height with 3 cm left aboveground) was set up in each observed plot (CK, CL and DS) to measure the components of ecosystem CO\({}_{2}\) exchanges, which are essential for calculating ecosystem CUE. The carbon exchange rates were measured using a cubic chamber (50 cm \(\times\) 50 cm \(\times\) 50 cm) attached to an infrared gas analyzer (LI-6400, LiCor, Lincoln, NE, USA). Two small fans were attached inside, at the top of the chamber, for air mixing during the measurements. Two temperature probes were used: one was inserted into the chamber to record the air temperature (AT), and the other one into the surrounding earth to the depth of 5 cm to record the soil temperature (ST). A portable soil-moisture device (TDR100, Spectrum, Plainfield, IL, USA) was introduced to record the soil-moisture (SM) content (0-10 cm) simultaneously. During the measurements, the transparent chamber was set on the metal base rim and two rings of seal pads were installed on the bottom edge of the chamber to prevent gas leakage. When measurements commenced, 30 consecutive recordings of CO\({}_{2}\) concentrations were taken for each chamber at 1 s intervals for 30 s. The CO\({}_{2}\) fluxes were calculated from the time series of changing concentrations. In the DS treatment plots, all roots were killed using glyphosate; this kind of herbicide can be transported from leaf tissues to the whole plant [30; 31], enabling the Rh to be directly determined for these plots. In contrast, in CL treatments, the roots would remain alive for some time [26] and the directly determined CO\({}_{2}\) exchanges were considered as belowground respiration (Rb), including Rh, root respiration, and soil animal respiration. The net ecosystem exchange (NEE) was determined in the CK plots. The calculation procedure in the LI-6400 manual (LiCor Inc., Lincoln, NE, USA, 2004) gives detailed instructions for these static chamber flux calculations. Following the measurement of NEE in the CK treatment plots, the chamber was vented, replaced on each frame, and covered with a piece of opaque cloth. The CO\({}_{2}\) exchange measurements were repeated, excluding light (therefore no photosynthesis), so as to obtain values representing Re. The difference between NEE and Re was considered to represent instantaneous gross ecosystem productivity (GEP) for the ecosystem in previous research [32]. Measurements were conducted on clear sunny days when standing live grassland biomass reached its peak (August). The observations were conducted continuously throughout the daytime at 1 h intervals. Observations were conducted on all the four blocks of each land-use pattern for 12 days and, therefore, there were 4 replicate days for every land-use pattern. The observation days were distributed alternatively among different ecosystems to ensure the comparability of data measured in similar weather conditions. As mentioned above, NEE, Re, Rh and Rb were directly determined in plots using standard methods [26; 29]. In our study, GEP was calculated with the sum of NEE and Re:  
\[\text{GEP}=-\text{Re}+\text{NEE} \tag{1}\]  
where GEP is the gross ecosystem productivity, Re is the respiration of the ecosystem, and NEE represents the net ecosystem exchange. Moreover, Re is the sum of Rab and Rb in vertical spatial sources. Alternatively, Re could be divided into the Ra and the Rh components to differentiate autotrophic and heterotrophic respiration sources. Since we directly determined Rb and Rh, we calculated Rab and Ra as follows:  
\[\text{Rab}=\text{Re}-\text{Rb} \tag{2}\]  
\[\text{Ra}=\text{Re}-\text{Rh} \tag{3}\]  
where Rab is the aboveground respiration, Rb is the belowground respiration, Ra is the autotrophic respiration, and Rh is the heterotrophic respiration. The belowground respiration represents the total soil microbial, plant root and soil animal respiration.