Spatial Variabillity of Soil Nitrogen Dynamics slong a Slope in a Cryptomeria japonica D.Don Plantation

Spatial variabillity of soil nitrogen(N) dynamics was examined along a slope in a 45-year-old Cryptomeria japonica D.Don plantation in the southeastern paet of Shiga Prefecture. Net N mineralization showed no clear gradient along the slope, while net nitrification and percent nitrification were high at lower positions,and very low at upper positions of the slope. Principal component(PC) analysis showed soil properties were divided into three groups which were PC1(water content and pH), and PC3(total C and N). Regressions of net soil N transformations against PCs scores suggested net N mincralization was mainly regulated by PC3, while net nitrification and percent nitrification were mainly regulated by PC1 and PC2. The difference in the main form of inorganic N was expected to affect soil N availability for plants through the difference in the mobility in negatively changed forest soil. We evaluated the soil N availability that reflebted the ion mobility factors by ion exchange resins and found that greater mobility of nitrate lead to greater soil N availability at lower positions of the slope. In addition, gross N transformations were directly measured using 15N isotope dilution, and the influence of microbial caebon (C) availability on the internal soil N cycles were examined by long-term laboratory incubation. Gross nitrifivation was detected in both soils taken at upper and lower positions on the slope, suggesting that nitrification was also an important process at upper positions where almost no net nitrification was detected. Changes in net and gross N transformations, the organic C and N pools, and microbial respiration suggested that start of rapid net nitrifibation might be affected not only by the availability of C for microbial biomass, but also by the relative availability of C and N

Nitrate-use traits of understory plants as potential regulators of vegetation distribution on a slope in a Japanese cedar plantation

[Background and Aims] Plant physiological traits and their relation to soil N availability was investigated as regulators of the distribution of understory shrub species along a slope in a Japanese cedar (Cryptomeria japonica) plantation in central Japan. [Methods]At the study site, previous studies demonstrated that both net and gross soil nitrification rates are high on the lower slope and there are dramatic declines in different sections of the slope gradient. We examined the distributions of understory plant species and their nitrate (NO3[-]-N) use traits, and compared the results with the soil traits. [Results]Our results show that boundaries between different dominant understory species correspond to boundaries between different soil types. Leucosceptrum stellipilum occurs on soil with high net and gross nitrification rates. Hydrangea hirta is dominant on soil with high net and low gross nitrification rates. Pieris japonica occurs on soil with very low net and gross nitrification rates. Dominant understory species have species-specific physiological traits in their use of NO3[-]-N. Pieris japonica lacks the capacity to use NO3[-]-N as a N source, but other species do use NO3[-]-N. Lindera triloba, whose distribution is unrelated to soil NO3[-]-N availability, changes the extent to which it uses NO3[-]-N in response to soil NO3[-]-N availability. [Conclusions]Our results indicate that differences in the physiological capabilities and adaptabilities of plant species in using NO3[-]-N as a N source regulate their distribution ranges. The identity of the major form of available soil N is therefore an environmental factor that influences plant distributions

The Potential of NO 3

Responses of seedlings of a shrub species, Lindera triloba, grown in perlite culture medium, to nitrate (NO3–-N) supply were investigated to estimate the saturating point of available NO3–-N for plant utilization. NO3–-N concentration and nitrate reductase activity (NRA) in leaves and roots were used as indicators of NO3–-N uptake and assimilation by L. triloba. Root NRA increased with NO3–-N supply when concentrations were low and reached a plateau at high NO3–-N concentrations. On the other hand, root NO3–-N concentration increased linearly with NO3–-N supply; therefore, it is suggested that NO3–-N uptake did not limit NO3–-N assimilation by L. triloba. In contrast, leaf NRA and leaf NO3–-N concentration were low and were not influenced by NO3–-N supply. This may be caused by the lack of transport of NO3–-N from roots to leaves. The NO3–-N retained in perlite was compared with NO3–-N pool sizes in soils from a forest where L. triloba occurs naturally to estimate the level of NO3–-N availability to plants in the forest soil. The maximum NO3–-N pool size in the forest soil was comparable to concentrations at which root NRA reached a plateau in perlite cultures. These results indicate that soil NO3–-N availability is below the saturation point for NO3–-N uptake by L. triloba, and it is the limiting factor of NO3–-N utilization by L. trilobaunder field conditions in which this species naturally occurs

Environmental Factors Controlling Leaf Emergence in Caragana microphylla, a Deciduous Shrub of the Mongolian Steppe

Abstract: We examined the effect of temperature and rainfall on the timing of leaf emergence in Caragana microphylla, a representative deciduous shrub found in the Mongolian steppe over a three-year period. Two peaks of leaf emergence were identified, the first of which appeared to be induced by temperature, while the second was controlled by rainfall

The Impact of Phenological Gaps on Leaf Characteristics and Foliage Dynamics of an Understory Dwarf Bamboo, Sasa kurilensis

Phenological gaps exert a significant influence on the growth of dwarf bamboos. However, how dwarf bamboos respond to and exploit these phenological gaps remain enigmatic. The light environment, soil nutrients, leaf morphology, maximum photosynthetic rate, foliage dynamics, and branching characteristics of Sasa kurilensis were examined under the canopies of Fagus crenata and Magnolia obovata. The goal was to elucidate the adaptive responses of S. kurilensis to phenological gaps in the forest understory. The findings suggest that phenological gaps under an M. obovata canopy augment the available biomass of S. kurilensis, enhancing leaf area, leaf thickness, and carbon content per unit area. However, these gaps do not appreciably influence the maximum photosynthetic rate, total leaf number, leaf lifespan, branch number, and average branch length. These findings underscore the significant impact of annually recurring phenological gaps on various aspects of S. kurilensis growth, such as its aboveground biomass, leaf morphology, and leaf biochemical characteristics. It appears that leaf morphology is a pivotal trait in the response of S. kurilensis to phenological gaps. Given the potential ubiquity of the influence of phenological gaps on dwarf bamboos across most deciduous broadleaf forests, this canopy phenomenon should not be overlooked

Natural 15 N Abundance of Plants and Soil N in a Temperate Coniferous Forest

Measurement of nitrogen isotopic composition (δ 15 N) of plants and soil nitrogen might allow the characteristics of N transformation in an ecosystem to be detected. We tested the measurement of δ 15 N for its ability to provide a picture of N dynamics at the ecosystem level by doing a simple comparison of δ 15 N between soil N pools and plants, and by using an existing model. δ 15 N of plants and soil N was measured together with foliar nitrate reductase activity (NRA) and the foliar NO 3 – pool at two sites with different nitrification rates in a temperature forest in Japan. δ 15 N of plants was similar to that of soil NO 3 – in the high-nitrification site. Because of high foliar NRA and the large foliar NO 3 – pool at this site, we concluded that plant δ 15 N indicated a great reliance of plants on soil NO 3 – there. However, many δ 15 N of soil N overlapped each other at the other site, and δ 15 N could not provide definitive evidence of the N source. The existing model was verified by measured δ 15 N of soil inorganic N and it explained the variations of plant δ 15 N between the two sites in the context of relative importance of nitrification, but more information about isotopic fractionations during plant N uptake is required for quantitative discussions about the plant N source. The model applied here can provide a basis to compare δ 15 N signatures from different ecosystems and to understand N dynamics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41374/1/10021_2002_Article_132.pd

スギ人工林内の斜面に沿った土壌窒素動態の空間的異質性

京都大学0048新制・課程博士博士(農学)甲第8030号農博第1080号新制||農||789(附属図書館)学位論文||H11||N3325(農学部図書室)UT51-99-T741京都大学大学院農学研究科地域環境科学専攻(主査)教授 武田 博清, 教授 谷 誠, 教授 小﨑 隆学位規則第4条第1項該当Doctor of Agricultural ScienceKyoto UniversityDA

Effects of fire-derived charcoal on soil properties and seedling regeneration in a recently burned Larix gmelinii/Pinus sylvestris forest

Purpose: Fire is a primary form of disturbance in boreal ecosystems. Charcoal is an important byproduct of forest fire and has been reported to have the potential to influence the plant community establishing after fire. To date, however, no study has effectively tested the relationship between charcoal and plant regeneration in the actual post-fire forests. To determine the contribution of charcoal to soil properties and plant regeneration after forest fires, we conducted in situ investigations concerning the relationship between charcoal and the plant-soil system. Materials and methods: We conducted a field investigation in a recently burnt Gmelin larch (Larix gmelinii)/Scots pine (Pinus sylvestris) forest in Russian Far East to investigate charcoal contents, pH water contents, and nutrient availability in soil together with the regeneration of larch and pine seedlings. Results and discussion: Positive correlations were found between charcoal contents and soil pH, water contents, and available P contents. Additionally, charcoal contents and number of pine seedlings were positively correlated. There was, however, no significant relationship between charcoal content and extractable NH4+ content or the number of larch seedlings. These results suggest that while charcoal influences are somewhat obscure in the field, charcoal significantly contributes to the amelioration of water and nutrient availability together with the success of regeneration of pine seedling. Conclusion: Charcoal produced during fire events in Gmelin larch and Scots pine forests of eastern Russia has a modest influence on soil properties, but has the potential to improve regeneration in these fire prone ecosystems