“双碳”目标下的农业碳问题研究进展及未来展望

减少农业碳排放,提高农业碳汇能力,是我国实现“双碳”目标的重要举措,也是潜力所在,故厘清农业碳问题的研究现状及其特征具有重要意义。为助力我国“双碳”目标早日实现,本文基于农业碳排放、农业碳汇以及农业低碳发展驱动因素3个维度对已有相关研究进行全面梳理：首先,明确了农业碳排放的基本概念并介绍了常见的测算方法,同时基于时序演变、空间分布、效率特征、减排路径等视角对其研究现状进行了回顾;其次,界定农业碳汇的基本概念,进而引申出森林碳汇、土壤碳汇和海洋碳汇并介绍各自的测算方法,而后则围绕农业净碳汇与碳汇市场化展开重点阐述;最后,从宏观和微观2个层面探讨影响农业低碳发展的主要因素,其中前者着眼于政策、经济、社会等方面,而后者则侧重于户主的内在因素和农户面临的外部环境。针对未来农业碳问题的研究方向,本文认为可重点围绕以下4个方面,即农业碳达峰的科学预测与差异化减排路径设计、农业减碳固碳潜力的科学评估与实现路径探讨、农业碳市场的构建与碳汇价值变现的思路探索以及农户低碳生产技术供需匹配探究与其制度优化。     

扁芝生物学特性的初步研究

通过对扁实（Ｅｌｆｖｉｎｇｉａａｐｐｌａｎａｔａ（Ｐｅｒｓ．ｅｘＧｒａｙ）Ｋａｒｓｔ＝Ｇａｎｏｄｅｒｍａ ａｐｐｌａｎｔｕｍ（Ｐｅｒｓ）．Ｐａｔ）生物学特性的研究,结果表明该菌在桦树汁培养基上生长最好,其次为ＰＤＡ;最适生长温度为３０℃,在ｐＨ＝３～８范围内均可生长,以ｐＨ＝４～５时生长最好;果糖和蔗糖是菌丝生长的最佳碳源,最佳氮源为脲素和天灭门冬素,无光照时菌丝生攻最好。     

Relationship between vegetation carbon storage and urbanization: A case study of Xiamen, China

Rapid growth of the Chinese urban population and the expansion of urban areas have led to changes in urban forest structure and composition, and consequently changes in vegetation carbon storage. The purpose of this study is to quantify the effects of urbanization on vegetation carbon storage in Xiamen, a city located in southern China. Data used for this study were collected from 39,723 sample plots managed according to the forest management planning inventory program. Data from these plots were collected in 4 non-consecutive years: 1972, 1988, 1996 and 2006. The study area was divided into three zones, which were defined according to their level of urbanization: the urban core, the suburban zone, and the exurban zone. Total vegetation carbon storage and the vegetation carbon density for each study period were calculated for each zone. Our results show that urban vegetation carbon storage has increased by 865,589.71 t during the period from 1972 to 2006 (34 years) in Xiamen, with a rapid increase between 1972 and 1996, then relatively little change between 1996 and 2006. The increase in vegetation carbon storage is mainly due to the large percentages of the suburban and exurban areas which exist in Xiamen city, and the implementation of reforestation programs in these two zones. The percentage of total regional carbon storage in the city center (urban core), suburbs and exurbs was 5%, 23% and 72%, respectively. This demonstrates that the exurbs store the majority of vegetation carbon, and thus play a critical role in the vegetation carbon storage of the study area. The intensification of urbanization in the future will likely expand the urban core and reduce the area of the suburbs and exurbs, and thus potentially decrease total vegetation carbon storage. This article concludes with a discussion of the implications of these results for vegetation carbon management and urban landscape planning.     

汉江水源区土地利用碳源/汇效应的空间差异分析——以陕南为例

梳理了土地利用碳源/汇途径,估算了2010年陕南不同土地利用方式的碳源/汇。结果表明:79%的碳源来自于建设用地;农作物、林业、林地碳汇分别占41.44%、31.12%、24.16%,区域碳吸收大于碳释放,净碳汇1 467 751 t C-eq;农作物碳汇区内差异很大,高值区在河谷地带,向两侧随高度增加递减,大巴山地高于秦岭山地;林业碳汇区内差异相对较小,河谷地带偏低,两侧山地区林业碳汇较高;两大盆地是净碳汇负值区,向周边山区碳汇逐渐增加,汉台区碳源密度值最高。     

果园生态系统碳循环规律研究进展

系统阐述了近10余年来果园生态系统碳循环规律的相关研究,得出以下结论:土壤是果园生态系统最大的碳库,碳储量占总体的70%以上;果园生态系统碳输入量大于碳输出量,是碳汇;经营管理措施对碳吸存影响较大,通过增施有机肥、生草、覆盖以及免耕等经营措施不但可以增加系统碳汇,减少碳排放,还可以提高果园土壤肥力。     

Response of soil microbial biomass and enzyme activities to the transient elevation of carbon dioxide in a semi-arid grassland

Although elevation of CO₂ has been reported to impact soil microbial functions, little information is available on the spatial and temporal variation of this effect. The objective of this study was to determine the microbial response in a northern Colorado shortgrass steppe to a 5-year elevation of atmospheric CO₂ as well as the reversibility of the microbial response during a period of several months after shutting off the CO₂ amendment. The experiment was comprised of nine experimental plots: three chambered plots maintained at ambient CO₂ levels of 360 μmol mol⁻¹ (ambient treatment), three chambered plots maintained at 720 μmol mol⁻¹ CO₂ (elevated treatment) and three unchambered plots of equal ground area used as controls to monitor the chamber effect.Elevated CO₂ induced mainly an increase of enzyme activities (protease, xylanase, invertase, alkaline phosphatase, arylsulfatase) in the upper 5 cm of the soil and did not change microbial biomass in the soil profile. Since rhizodeposition and newly formed roots enlarged the pool of easily available substrates mainly in the upper soil layers, enzyme regulation (production and activity) rather than shifts in microbial abundance was the driving factor for higher enzyme activities in the upper soil. Repeated soil sampling during the third to fifth year of the experiment revealed an enhancement of enzyme activities which varied in the range of 20-80%. Discriminant analysis including all microbiological properties revealed that the enzyme pattern in 1999 and 2000 was dominated by the CO₂ and chamber effect, while in 2001 the influence of elevated CO₂ increased and the chamber effect decreased.Although microbial biomass did not show any response to elevated CO₂ during the main experiment, a significant increase of soil microbial N was detected as a post-treatment effect probably due to lower nutrient (nitrogen) competition between microorganisms and plants in this N-limited ecosystem. Whereas most enzyme activities showed a significant post-CO₂ effect in spring 2002 (following the conclusion of CO₂ enrichment the previous autumn, 2001), selective depletion of substrates is speculated to be the cause for non-significant treatment effects of most enzyme activities later in summer and autumn, 2002. Therefore, additional belowground carbon input mainly entered the fast cycling carbon pool and contributed little to long-term carbon storage in the semi-arid grassland.     

Carbon and nitrogen mineralization as affected by drying and wetting cycles

Drying and rewetting of soil is an important process in soil aggregation, soil organic matter (SOM) decomposition, and nutrient cycling. We investigated the source of the C and N flush that occurs upon rewetting of dry soil, and whether it is from microbial death and/or aggregate destruction. A moderately well drained Kennebec silt loam (Fine-silty, mixed, superactive, mesic Cumulic Hapludoll) was sampled to a 10 cm depth. Soil under constant water content (CWC) was compared with soil subjected to a series of four dry-wet (DW) cycles during the experimental period (96 d) and incubated at 25 °C. Mineralized C and N were measured during the drying and rewetting periods. Aggregate size distributions were studied by separating the soil into four aggregate size classes (>2000, 250-2000, 53-250, and 20-53 μm) by wet sieving. Repeated DW cycles significantly reduced cumulative N mineralization compared with CWC. The reduction in cumulative mineralized C resulting from DW compared with CWC increased as the DW treatments were subjected to additional cycles. The flush of mineralized C significantly decreased with repeated DW cycles. There was no significant effect on aggregate size distributions resulting from to the DW cycles compared with CWC treatment. Therefore, the flush of mineralized C and N seemed to be mostly microbial in origin in as much as aggregate distribution was unaffected by DW cycles.     

Post-Flowering Photoperiod Effects on Reproductive Development and Agronomic Traits of Long-Day and Short-Day Crops

Pre-flowering photoperiod effects on floral initiation, flowering time and yield components of various crops have been well studied, but the post-flowering photoperiod effects on major field crops are not clearly understood. A controlled environment study was carried out using six long-day (LD) crops, flax, sugar beet, broad bean, triticale, wheat, and rapeseed, and seven short-day (SD) crops including Adzuki bean, potato, rice, peanut, mungbean, cotton and corn with a major objective of evaluating the post-flowering photoperiod effects on their reproductive development and yield components. There were significant inter- and intra-specific differences in their response to post-flowering photoperiod treatments. The effects of short days on LD crops were similar to LD effects on SD crops. The post-flowering duration was prolonged by short photoperiod in LD crops and long photoperiod in SD crops. There was, however, significant genotypic variation within a species for such effects. The post-flowering LD treatment caused abscission of flowers and pods and the resumption of vegetative growth in Adzuki bean. The post-flowering LD treatment also delayed the shoot senescence of one of the two potato varieties and decreased the number of tubers per plant in both varieties. The LD treatment delayed maturation of rice and mungbean, and decreased seed yield and 100-seed weight of peanut, although the shoot senescence of peanut was not apparently affected. Rapeseed, wheat, cotton and corn genotypes in this study did not show any sensitivity to post-flowering photoperiod. In triticale (an LD crop) exposure to short photoperiod post-flowering increased the number of spikes per plant perhaps due to a greater assimilate accumulation over a longer duration. The results from the current study as well as those from our previous experiments suggest that post-flowering photoperiod responses do exist in diverse field crops, and that there are strong genotypic differences in sensitivity and magnitude of response to post-flowering photoperiod. Photoperiod after flowering substantially regulates the source/sink relationship, and promotes partitioning and accumulation of assimilates to storage organs of crops when it favours the reproductive development of crops.     

对我国活性炭工业发展的几点思考

对我国活性炭工业的历史和现状进行了回顾，对发展我国活性炭事业提出了若干意见和建议。     

The present status of “quick tests” for on-farm analysis with emphasis on manures and soil: What is available and what is lacking?

There is an increasing interest in on-farm testing of a variety of materials, from soils to materials produced or utilized on the farm, including manure. Among the issues to consider are selection of constituents of interest, e.g., fiber and protein in forages versus inorganic-and organic-N and P in manures; the nature of the testing, e.g., conventionally based assays using solutions or test strips versus portable instruments; the potential advantages or disadvantages of on-farm versus conventional laboratory testing, such as speed, timeliness, waste generation, and cost. The availability of on-farm testing methods varies greatly with both the media in question and the analyte of interest. For example, for manures several quick tests exist for the determination of total ammoniacal N (TAN) which can be quite accurate (R² of .9 or better versus laboratory determinations), fast and reasonably inexpensive, while no such methods exist for the determination of organic-N in the same samples. No quick test has been found satisfactory for the determination of P or K in dairy or poultry manures, although excellent results have been obtained for swine manure. Similarly, soil test kits have existed for years for determining N, P and K, but no such test exists for determining soil C content (organic or inorganic), and no inexpensive method exists for forage quality determinations (fiber, protein, digestibility). Spectroscopic methods such as near-and mid-infrared spectroscopy have found increasing use in the laboratory for the rapid analysis of a wide variety of products including feeds, manures and soils and offer great potential for on-farm determinations. This paper discusses the present state, and future potential, of methods suitable for on-farm testing of the wide variety of materials from soils to those materials utilized or produced on a farm, with emphasis on manures and soils and spectroscopic methods.