Simulating leaf net CO_2 assimilation rate of C_3 & C_4 plants and its response to environmental factors

Basic structure and algorithm of leaf mechanism photosynthesis model were described in first part of this study based on former researcher results. Then, considering some environmental factors influencing on leaf photosynthesis, three numerical sensitivity experiments were carried out. We simulated the sing le leaf net CO2 assimilation, which acts as a function of different light, carbo n dioxide and temperature conditions. The relationships between leaf net photosy nthetic rate of C3 and C4 plant with CO2 concentration intercellular, leaf tempe rature, and photosynthetic active radiation (PAR) were presented, respectively. The results show the numerical experiment may indicate the main characteristic o f plant photosynthesis in C3 and C4 plant, and further can be used to integrate with the regional climate model and act as land surface process scheme, and bett er understand the interaction between vegetation and atmosphere.

Simulating leaf net CO2 assimilation rate of C3 & C4 plants and its response to environmental factors

Basic structure and algorithm of leaf mechanism photosynthesis model were described in first part of this study based on former researcher results. Then, considering some environmental factors influencing on leaf photosynthesis, three numerical sensitivity experiments were carried out. We simulated the sing le leaf net CO2 assimilation, which acts as a function of different light, carbo n dioxide and temperature conditions. The relationships between leaf net photosy nthetic rate of C3 and C4 plant with CO2 concentration intercellular, leaf tempe rature, and photosynthetic active radiation (PAR) were presented, respectively. The results show the numerical experiment may indicate the main characteristic o f plant photosynthesis in C3 and C4 plant, and further can be used to integrate with the regional climate model and act as land surface process scheme, and bett er understand the interaction between vegetation and atmosphere.

黄土高原西部地区末次冰期和全新世有机碳同位素变化与C_3/C_4植被类型转换研究

文章利用黄土高原西缘代表性的塬堡剖面有机碳同位素数据,估算了末次冰期以来地表植被中C3/C4植 物的相对丰度,指示出研究区域末次冰期几乎为纯粹的C3植物,而全新世为C3植物占优势的C3和C4混合植被类 型。温度是控制中国黄土高原C4植物是否发生的关键性气候因素,末次冰期向全新世转化过程中存在的某“阈值 温度”控制了两种植被类型的存在。全新世土壤有机碳同位素偏正于末次冰期,符合前人研究得到的认识。末次 冰期间冰段(MIS3)至盛冰期,土壤有机碳同位素为偏正变化趋势,符合现代C3植物本身随气候条件改变的碳同位 素组成变化。研究表明,利用黄土-古土壤有机碳同位素进行古气候变化研究,不能只将有机碳同位素简单的解 释为C3/C4植物相对丰度的变化,在单一植被类型下,还需要考虑植物本身碳同位素组成随气候条件的变化;另外, 研究还说明,我国黄土高原不同地区同时段土壤有机碳同位素值可以不同,其变化可以不具有相同的趋势,因此, 简单将有机碳同位素偏正归因于夏季风增强是值得商榷的。

中国东北草原植物中的C_3和C_4光合作用途径

以光合作用关键羧化酶ＰＥＰＣ和ＲｕＢＰＣ活性比，并且参照叶片ＣＯ２补偿浓度，δ１３Ｃ值和叶片解剖结构特点来鉴定东北草原区２３３种植物的Ｃ３，或Ｃ４光合作用途径。这些植物隶属于１４４属３７科，其中１３７种为首次鉴定。８９种具有Ｃ４光合作用途径，隶属于５５属１７科；１４４种具有Ｃ３光合作用途径，隶属于９４属２８科。大多数Ｃ４种分布在禾本科（Ｐｏａｃｅａｅ）、莎草科（Ｃｙｐｅｒａｃｅａｅ）、苋科（Ａｍａｒａｎｔｈａｃｅａｅ）和藜科（Ｃｈｅｎｏｐｏｄｉ－ａｃｅａｅ）。苋属（Ａｍａｒａｎｔｈｕｓ）、地肤属（Ｋｏｃｈｉａ）、狗尾草属（Ｓｅｔａｒｉａ）和虎尾草属（Ｃｈｌｏｒｉｓ）中的均为Ｃ４植物。Ｃ４植物的生境多为干草原和盐碱草地，而Ｃ３植物则主要分布于草甸草原和干草原。然而，Ｃ４植物对热。

C_3植物中C_4途径的研究进展

综述了Ｃ３植物中Ｃ４途径的发现及研究现状；阐述了Ｃ３植物中Ｃ４途径的几种作用机理；根据Ｃ３植物中Ｃ４途径的存在，探讨了改造Ｃ３植物的遗传特性；

判别分析方法在鉴别C_3 、C_4植物中的应用——以中国东北样带 (NECT)的研究为例

判别分析是多元统计分析中判断个体所属类型的一种重要方法。以中国东北样带(NECT)作为研究平台,利用判别分析鉴别植物光合功能型。采用国际上先进的植物光合测定系统LCA4便携式光合仪和CID_203便携式叶面积仪在野外所测定的植物生理生态参数,选取51个来自C3功能群的植物种和15个来自C4功能群的植物种构建判别模型,进行光合碳同化途径的判别。用马氏距离和后验概率判别准则进行回判,准确率达到98.48%。利用此判别模型可以根据任一植物的光合速率、蒸腾速率。

C_3、C_4及CAM植物的光合速率日变化及叶绿素含量的比较

在夏季高温条件下 ,棉花 (C3 植物 )、玉米 (C4植物 )的光合速率日变化曲线均为双峰型 ;落地生根(CAM植物 )的光合速率日变化曲线为单峰型。这 3种植物的叶绿素含量及叶绿素a b的值均不相同 ,其中玉米叶绿素含量及其a b的值均最大 ,棉花叶绿素含量比落地生根的高 ,因此叶绿素含量及其a b值的不同可能是导致其光合速率的差异和光合速率日变化曲线型不同的重要原因。

甘蔗C_4磷酸烯醇式丙酮酸羧化酶基因植物表达载体构建

根据用于转化的甘蔗 C4Ppc基因的特点 ,分别构建了无启动子、35 S启动子、2 x35 S启动子的植物表达载体 p BIpepc、p L Apepc、p CBIpepc;用盐冻融法将其导入农杆菌 LBA4 40 4 ,可用于烟草、水稻、大豆、甘薯等 C3 作物遗传转化。

Climate as the dominant control on C_3 and C_4 plant abundance in the Loess Plateau: Organic carbon isotope evidence from the last glacial-interglacial loess-soil sequences

Abundance of C3 and C4 photosynthesis plants can be inferred relatively from stable carbon isotopic composi-tion of organic matter in soils. The samples from five sequences of the last glacial-interglacial loess-soil in the Chinese Loess Plateau have been measured for organic carbon isotopic ratios (d 13Corg). The organic carbon isotope data show that relative abundance (or biomass) of C4 plants was increased ca. 40% for each sampling site from the last glacial maximum (LGM) to Holocene optimum, and increased southeastward on the Loess Plateau during both periods of LGM and Holocene. Statistic analyses on the steady maximum d 13Corg values of Holocene soils and modern climatic data from the Loess Plateau and Inner Mongolia indicate that the C4 plant abundance increases with increasing temperature and decreasing precipitation. The C4 plant abundance is related much closer with mean April tem-perature and precipitation than annual. These results lead us to deduce following conclusions. First, temperature is the major factor for control on variations in C4 plant abundance in the Loess Plateau from the last glacial to interglacial. In the absence of favorable temperature condition, both of low moisture and low atmospheric CO2 concentration are insufficient to drive an expansion of the C4 plants in the plateau. Second, d 13Corg in the loess-paleosol sequences, as a proxy of the relative abundance of C4 plants in the Loess Plateau, could not be used as an indicator of changes in the summer monsoon intensity unless the tem-perature had changed without great amplitude. Since all C4 plants are grasses, finally, the increase of the C4 plants supports that forest has not been dominant in the ecosystem on the Loess Plateau during Holocene although precipitation and atmospheric CO2 were largely increased relative to those during LGM.

Distribution of C_4 plants along the Northeast China transect and its correlation to the environmental factors

The distribution of C4 plants and the C4/C3 ratio along Northeast China transect （NECT） have been studied. A model to quantify their relation with environmental factors has been set up. The ratio of the number of C4 plants to that of C3 plants along NECT shows two low and two high trends from east to west, and their distribution is mainly decided by annual average temperature and precipitation.

Variations in carbon isotope ratios of C_3 plants and distribution of C_4 plants along an altitudinal transect on the eastern slope of Mount Gongga

Variations in carbon isotopic ratios (δ 13C) of C3 plants and distribution of C4 plants were investigated along an altitudinal transect on the eastern slope of Mount Gongga, and the environmental effects on them were discussed. It is shown that plants with C4 photosynthetic pathway mainly occur at altitudes below 2100 m a.s.l., suggesting that the low summer temperature is responsible for the distributional pattern. In addition, δ 13C of C3 plants increases with elevation at the region above 2000 m a.s.l. with the characteristics of humid climate, and the increase rate in δ 13C for C3 plants is about 1.3‰ per kilometer. Temperature determines the altitudinal trend of δ 13C.

Analysis of carbon isotope in phytoliths from C3 and C4 plants and modern soils

The analysis of carbon isotope in phytoliths from modern plants and surface soils in China shows that the values of carbon isotope are consistent with those from C3 and C4 plants, and the processes of photosynthesis of the original plants can be clearly identified by carbon isotope in phytoliths. The value of carbon isotope varied from -23.8‰ to -28‰, with the maximum distributed in the latitude zone from 34°N to 40°N in North China and East China areas, and the minimum in the Northeast China and South China regions. The values of carbon of phytoliths tend to increase from low to high and then reduce to low value again as the latitude increases. In the same latitude zone, the carbon isotope in phytoliths from grassland soil under the trees is obviously lower than that from grassland soil without any trees with the difference of 1‰ - 2‰.

Contribution of the Alternative Respiratory Pathway to PSII Photoprotection in C3 and C4 Plants

The mechanism by which the mitochondrial alternative oxidase （AOX） pathway contributes to photosystem II （PSII） photoprotection is in dispute. It was generally thought that the AOX pathway protects photosystems by dissipating excess reducing equivalents exported from chloroplasts through the malate/oxaloacetate （Mal/OAA） shuttle and thus preventing the over-reduction of chloroplasts. In this study, using the aoxla Arabidopsis mutant and nine other C3 and C4 plant species, we revealed an additional action model of the AOX pathway in PSII photoprotection. Although the AOX pathway contributes to PSII photoprotection in C3 leaves treated with high light, this contribution was observed to disappear when photorespiration was suppressed. Disruption or inhibition of the AOX pathway significantly decreased the photorespiration in C3 leaves. Moreover, the AOX pathway did not respond to high light and contributed little to PSII photoprotection in C4 leaves possessing a highly active Mal/OAA shuttle but with little photorespiration. These results demonstrate that the AOX pathway contributes to PSII photoprotection in C3 plants by maintaining photo- respiration to detoxify glycolate and via the indirect export of excess reducing equivalents from chloro-plasts by the MaI/OAA shuttle. This new action model explains why the AOX pathway does not contribute to PSII photoprotection in C4 plants.

Response of root traits of Reaumuria soongorica and Salsola passerina to facilitation

C3 plant Reaumuria soongorica and C4 plant Salsola passerina are super xerophytes and coexist in a mixed community in either isolated or associated growth, and interspecific facilitation occurs in associated growth. In the present study, the root traits including root distribution, root length（RL）, root surface area（RSA）, root weight（RW） and specific root length（SRL） of both species in two growth forms were investigated to clarify their response to facilitation in associated growth. Six isolated plants of each species, as well as six associated plants similar in size and development were selected during the plant growing season, and their roots were excavated at 0–10, 10–20, 20–30, 30–40 and 40–50 cm soil depths at the end of the growing season. All the roots of each plant were separated into the two categories of fine roots（2 mm diameter） and coarse roots（≥2 mm diameter）. Root traits such as RL and RSA in the fine and coarse roots were obtained by the root analyzing system WinRHIZO. Most of the coarse roots in R. soongorica and S. passerina were distributed in the top 10 cm of the soil in both growth forms, whereas the fine roots of the two plant species were found mainly in the 10–20 and 20–30 cm soil depths in isolated growth, respectively. However, the fine roots of both species were mostly overlapped in 10–20 cm soil depth in associated growth. The root/canopy ratios of both species reduced, whereas the ratios of their fine roots to coarse roots in RL increased, and both species had an increased SRL in the fine roots in associated growth. In addition, there was the increase in RL of fine roots and content of root N for S. passerina in associated growth. Taken together, the root growth of S. passerina was facilitated for water and nutrient exploration under the interaction of the overlapped roots in both species in associated growth, and higher SRL allowed both species to more effectively adapt to the infertile soil in the desert ecosystem.

The effect of C3 and C4 plants for the magnetic susceptibility signal in soils

To understand the origin of the ultrafine pedogenic components responsible for the magnetic susceptibility (MS) enhancement remains a major challenging problem in linking magnetic signal with paleoclimate. Here we examine the effect of the natural fires on the MS signal of both plants and modern soils and in particular the MS difference between C3 and C4 plant ashes and their influence on magnetic susceptibility. We also proved the influence of the different floral root systems on the MS signal of modern soils. We find that the C3 and C4 plants are different in their ability to enhance MS signal of modern soils. Increased MS signal of modern soils by C4 plants was much greater than that by C3 plants.

Soil Carbon Dynamics Under Changing Climate A Research Transition from Absolute to Relative Roles of Inorganic Nitrogen Pools and Associated Microbial Processes:A Review

It is globally accepted that soil carbon （C） dynamics are at the core of interlinked environmental problems, deteriorating soil quality and changing climate. Its management remains a complex enigma for the scientific community due to its intricate relationship with soil nitrogen （N） availability and moisture-temperature interactions. This article reviews the management aspects of soil C dynamics in light of recent advances, particularly in relation to the availability of inorganic N pools and associated microbial processes under changing climate. Globally, drastic alterations in soil C dynamics under changing land use and management practices have been primarily attributed to the variation in soil N availability, resulting in a higher decomposition rate and a considerable decline in soil organic C （SOC） levels due to increased soil CO2 emissions, degraded soil quality, and increased atmospheric CO2 concentrations, leading to climate warming. Predicted climate warming is proposed to enhance SOC decomposition, which may further increase soil N availability, leading to higher soil CO2 effiux. However, a literature survey revealed that soil may also act as a potential C sink, if we could manage soil inorganic N pools and link microbial processes properly. Studies also indicated that the relative, rather than the absolute, availability of inorganic N pools might be of key importance under changing climate, as these N pools are variably affected by moisture-temperature interactions, and they have variable impacts on SOC turnover. Therefore, multi-factorial studies are required to understand how the relative availability of inorganic N pools and associated microbial processes may determine SOC dynamics for improved soil C management.

An Invasive Succulent Plant (Kalanchoe daigremontiana) Influences Soil Carbon and Nitrogen Mineralization in a Neotropical Semiarid Zone

It has long been recognized that plant invasions may alter carbon （C） and nitrogen （N） cycles, but the direction and magnitude of such alterations have been rarely quantified. In this study, we quantified the effects caused by the invasion of a noxious exotic plant, Kalanchoe daigrernontiana （Crassulaceae）, on C and N mineralization and enzymatic and microbial activities in the soil of a semiarid locality in Venezuela. We compared soil parameters associated with these processes （C and N mineralization time and the cumulative values, fluorescein diacetate hydrolytic activity, and activities of dehydrogenase, β-glucosidase, glucosaminidase, and urease） between invaded and adjacent non-invaded sites. In addition, correlations among these parameters and the soil physical-chemical properties were also examined to determine if a positive feedback exists between nutrient availability and K. daigremontiana invasion. Overall, our results showed that C mineralization and transformation of organic compounds to NH4^＋ were favored at sites colonized by K. daigrernontiana. With this species, we found the highest cumulative amounts of NH4^＋-N and C and the lowest mineralization time. These results could be explained by higher activities of urease and glueosaminidase in soils under the influence of K. daigremontiana. In addition, higher amounts of organic matter and moisture content in invaded soils might favor C and N mineralization. In conclusion, invasion of Neotropical semiarid zones by K. daigrernontiana may influence the chemical and biological properties of the soils covered by this species, increasing nutrient bioavailability, which, in time, can facilitate the invasion process.

Increased winter-spring precipitation from the last glaciation to the Holocene inferred from a δ^(13)C_(org) record from Yili Basin(Xinjiang, NW China)

The nature and dynamics of climate change in central Asia since the late Pleistocene are controversial. Moreover,most of the published studies focus mainly on the evolution of moisture conditions, and there have been few attempts to address changes in seasonality. In this study, records of δ^(13)C_(org), TOC, TN, C/N and grain size were obtained from lacustrine sediments at Yili Basin, Xinjiang, NW China. Our aim was to reconstruct the trend in seasonality of precipitation from the last glaciation to the Holocene. The organic matter content of the sediments is derived predominantly from terrestrial plants. The δ^(13)C_(org)values vary from-19.4‰ to-24.8‰, indicating that the vegetation was dominated by C_3 plants. Winter-spring precipitation is identified as the factor determining the relative proportions of C_3 and C_4 plants in the region. A negative trend in δ^(13)C_(org)corresponding to an increase in the relative abundance of C_3 plants indicate a trend of increasing winter-spring precipitation from the last glaciation to the Holocene. The increased incidence of wintertime storms in the interior of Asia is suggested to result in the increase of winterspring precipitation in the Holocene.

玉米稻的光合效率分析

采用离子束介导方法获得的玉米稻株系，其光合速率较原品种提高２９．２％～１３１．７％，平均提高８４．０％。离子束介导是高光效育种的一条有效途径。

Carbon isotopic records in paleosols over the Pliocene in Northern China: Implication on vegetation development and Tibetan uplift

Carbon isotopic composition of pedogenic carbonate can be used to estimate the proportion of C4 and C3 plants. Here we present carbon isotopic data of carbonate in a red earth section at Xifeng, central Loess Plateau. Results show that C4 vegetation increased in -4.4 Ma B.P., stabilized between 4.0 and 3.0 Ma B.P. The character and timing of C4 expansion on the Loess Plateau are similar, but different with other localities, e.g. Pakistan and Africa, implying that regional climate changes were main factors driving the expansion of C4 plants. This event is comparable in timing with increased aridity evidenced by Xifeng grain size and North Pacific eolian dust records. Therefore we argue that the Pliocene expansion of C4 plants in northern China might have been caused by the increased aridity, which in turn might be related to rapid uplift of the Tibetan Plateau.