Effects of Elevated CO2 and N Addition on Growth and N2 Fixation of a Legume Subshrub (Caragana microphylla Lam.) in Temperate Grassland in China

It is well demonstrated that the responses of plants to elevated atmospheric CO2 concentration are species-specific and dependent on environmental conditions. We investigated the responses of a subshrub legume species, Caragana microphylla Lam., to elevated CO2 and nitrogen (N) addition using open-top chambers in a semiarid temperate grassland in northern China for three years. Measured variables include leaf photosynthetic rate, shoot biomass, root biomass, symbiotic nitrogenase activity, and leaf N content. Symbiotic nitrogenase activity was determined by the C2H2 reduction method. Elevated CO2 enhanced photosynthesis and shoot biomass by 83% and 25%, respectively, and the enhancement of shoot biomass was significant only at a high N concentration. In addition, the photosynthetic capacity of C. microphylla did not show down-regulation under elevated CO2. Elevated CO2 had no significant effect on root biomass, symbiotic nitrogenase activity and leaf N content. Under elevated CO2, N addition stimulated photosynthesis and shoot biomass. By contrast, N addition strongly inhibited symbiotic nitrogenase activity and slightly increased leaf N content of C. microphylla under both CO2 levels, and had no significant effect on root biomass. The effect of elevated CO2 and N addition on C. microphylla did not show interannual variation, except for the effect of N addition on leaf N content. These results indicate that shoot growth of C. microphylla is more sensitive to elevated CO2 than is root growth. The stimulation of shoot growth of C. microphylla under elevated CO2 or N addition is not associated with changes in N2-fixation. Additionally, elevated CO2 and N addition interacted to affect shoot growth of C. microphylla with a stimulatory effect occurring only under combination of these two factors

Impact of Green Credit Incentives on Operational Decisions of Green Supply Chain

Financial incentives have been introduced to guide financial institutions to increase green credit allocation, strengthen environmental risk management, and enhance support for green and low-carbon development. This paper investigated the government’s support for the carbon-emission supply chain by implementing green credit incentives. Two financial incentives are explored: performance-based incentives and interest subsidies. We conduct game-theoretic models to examine the characteristics and effects of two financial incentives on the supply chain. Our results reveal that: (1) both incentives are effective in scaling up supply chain performance and stimulate investment in emission reduction, while the mechanism differs according to the direct beneficiaries; (2) performance-based incentives are more sensitive to environmental damage, while the optimal subsidy ratio is more sensitive to consumer green awareness, indicating that the bank has an instinctive aversion to the risks inherent in abatement investments; (3) it is optimal for the government to intervene in green credit financing activities when environmental advantages and costs and consumer green consciousness are recognized. Our conclusions suggest the government can determine financial incentives for green credit based on the stage of green transition development and the real, demanding requirements of transition goals.   Received: 7 September 2023 | Revised: 4 December 2023 | Accepted: 15 January 2024   Conflicts of Interest  The authors declare that they have no conflicts of interest to this work.   Data Availability Statement Data is available on request from the authors

A handheld device for measuring the diameter at breast height of individual trees using laser ranging and deep-learning based image recognition

Background Accurate and efficient measurement of the diameter at breast height (DBH) of individual trees is essential for forest inventories, ecological management, and carbon budget estimation. However, traditional diameter tapes are still the most widely used dendrometers in forest surveys, which makes DBH measurement time-consuming and labor-intensive. Automatic and easy-to-use devices for measuring DBH are highly anticipated in forest surveys. In this study, we present a handheld device for measuring the DBH of individual trees that uses digital cameras and laser ranging, allowing for an instant, automated, and contactless measurement of DBH. Results The base hardware of this device is a digital camera and a laser rangefinder, which are used to take a picture of the targeted tree trunk and record the horizontal distance between the digital camera and the targeted tree, respectively. The core software is composed of lightweight convolutional neural networks (CNNs), which includes an attention-focused mechanism for detecting the tree trunk to log the number of pixels between the edges. We also calibrated the digital camera to correct the distortion introduced by the lens system, and obtained the normalized focal length. Parameters including the horizontal distance between the digital camera and the targeted tree, number of pixels between the edges of the tree trunk, and normalized focal length were used to calculate the DBH based on the principles of geometrical optics. The measured diameter values, and the longitudes and latitudes of the measurement sites, were recorded in a text file, which is convenient to export to external flash disks. The field measurement accuracy test showed that the BIAS of the newly developed device was - 1.78 mm, and no significant differences were found between the measured diameter values and the true values (measured by the conventional tape). Furthermore, compared with most other image-based instruments, our device showed higher measurement accuracy. Conclusions The newly developed handheld device realized efficient, accurate, instant, and non-contact measurements of DBH, and the CNNs were proven to be successful in the detection of the tree trunk in our research. We believe that the newly developed device can fulfill the precision requirement in forest surveys, and that the application of this device can improve the efficiency of DBH measurements in forest surveys

Effects of grazing on CO2, CH4, and N2O fluxes in three temperate steppe ecosystems

Terrestrial ecosystems play a critical role in regulating the emission and uptake of the most important greenhouse gases (GHGs) such as CO2, CH4, and N2O. However, the effects of grazing on these GHG fluxes in different steppe types remain unclear. Here, we compared the effects of grazing on seasonal CO2, CH4, and N2O fluxes in the meadow (MS), typical (TS), and desert (DS) temperate steppe ecosystems in northern China. CO2 emission rates increased from 311.4 +/- 73.2 to 349.6 +/- 55.4 mg.m(-2).h(-1) in MS, but decreased in TS (from 341.3 +/- 93.0 to 239.5 +/- 81.9 mg.m(-2).h(-1)) and DS ( from 212.1 +/- 53.7 to 163.0 +/- 83.4 mg.m(-2).h(-1)) in response to summer grazing (SG). N2O emission rates increased in MS from 4.7 +/- 2.2 to 8.1 +/- 3.4 mu g.m(-2).h(-1), but not significantly changed in TS (9.2 +/- 4.2 vs. 8.4 +/- 2.4 mu g.m(-2).h(-1)) and DS (6.3 +/- 1.5 vs. 5.7 +/- 1.6 mu g.m(-2).h(-1)) by SG. CH4 uptake rates increased in MS from 33.0 +/- 11.7 to 47.1 +/- 10.4 mu g.m(-2).h(-1) and decreased from 64.4 +/- 7.6 to 56.2 +/- 5.9 mu g.m(-2).h(-1) in TS in response to SG. In MS and DS, N2O emissions were positively related to seasonal CO2 emissions and negatively related to CH4 uptakes. No significant relationships were found between GHG fluxes in TS. Summer grazing did not affect the relationship between CO2 and N2O emissions in MS, but reduced the relationship by enhancing the effect of aboveground biomass (AGB) on N2O emission in DS. The significant negative relationship between CH4 uptake and N2O emission in MS and DS could be attributed to the significant relationship between soil temperature (ST) and AGB in MS and to the significant effects of soil moisture on both CH4 uptake and N2O emission in DS. The decrease in the magnitude of the correlation coefficients between CH4 uptake and N2O emission by SG was due to the negative relationship between ST and AGB simultaneously in MS and DS. Our results suggest that effects of SG on GHG fluxes varied in different steppes and the relationship among GHGs was steppe-dependent and SG also changed the relationship by affecting GHG fluxes induced by varied soil and environmental factors

Foliar uptake of dew in the sandy ecosystem of the Mongolia Plateau: A life-sustaining and carbon accumulation strategy shared differently by C-3 and C-4 grasses

Dew is an important source of available water in arid or semi-arid areas and considerable attention has focused upon whether foliar dew uptake occurs. Nonetheless, its occurrence and effects on plant growth in the sand-based ecosystems of the Mongolia Plateau are largely unknown. We performed laboratory experiments and conducted a three-year field investigation of dew in the Hunshandak sandland, northern China. Dew yield was determined by a weighing method. The ecological significance of dew was evaluated by measuring isotopes in the field, leaf water content, photosynthesis and the biomass of drought-stressed plants exposed to dew. Nights producing dew comprised 53% of those between June and October when the atmospheric relative humidity was higher than 80% and wind speed was lower than 4.0 m s(-1). Dew yield averaged 0.15 mm night(-1) and its maximum value was 0.30 mm night(-1). When exposed to dew, drought-stressed plants increased leaf relative water content and net photosynthetic rate (P-n) between 5-76% and 5-240% for C-3 plants, and 3-18% and 5-109% for C-4 plants. Dew produced more root and total biomass (15-81% and 24-82%) in C-4 species than in C-3 species (3-28% and 5-25%). Regular dew events on five or more consecutive nights in seven days can sustain C-3 species, while C4 species accumulate more carbon resources. This study found that the high dew yield in arenicolous ecosystems was due to the soil matrix and environmental differences in the neighboring steppe ecosystem. C-4 species and drought resistant C-3 species displayed higher efficiency for dew utilization than the moderately drought resistant C-3 species. This may affect the plant community's dynamic and ecological interactions in response to future climate change

TECHNICAL REPORTS: PLANT AND ENVIRONMENT INTERACTIONS Responses of a Dominant Temperate Grassland Plant (Leymus chinensis) to Elevated Carbon Dioxide and Nitrogen Addition in China

The impact of elevated atmospheric C