Soil phosphorus budget in global grasslands and implications for management

Grasslands, accounting for one third of the world terrestrial land surface, are important in determining phosphorus (P) cycle at a global scale. Understanding the impacts of management on P inputs and outputs in grassland ecosystem is crucial for environmental management since a large amount of P is transported through rivers and groundwater and detained by the sea reservoir every year. To better understand P cycle in global grasslands, we mapped the distribution of different grassland types around the world and calculated the corresponding P inputs and outputs for each grassland type using data from literature. The distribution map of P input and output revealed a non-equilibrium condition in many grassland ecosystems, with: (i) a greater extent of input than output in most managed grasslands, but (ii) a more balanced amount between input and output in the majority of natural grasslands. Based on the mass balance between P input and output, we developed a framework to achieve sustainable P management in grasslands and discussed the measures targeting a more balanced P budget. Greater challenge is usually found in heavily-managed than natural grasslands to establish the optimum amount of P for grass and livestock production while minimizing the adverse impacts on surface waters. This study provided a comprehensive assessment of P budget in global grasslands and such information will be critical in determining the appropriate P management measures for various grassland types across the globe

Plant Canopy May Promote Seed Dispersal by Wind

Seed dispersal has received much research attention. The plant canopy can intercept diaspores, but the effect of the plant canopy (the aboveground portion of a plant consisting of branches and leaves) on dispersal distance has not been explored empirically. To determine the effect of plant canopy on seed dispersal distance, a comparison of diaspores falling through open air and through plant canopy was made in a wind tunnel using three wind speeds and diaspores with various traits. Compared with diaspores falling through open air, the dispersal distance of diaspores falling through plant canopy was decreased or increased, depending on wind speed and diaspore traits. When falling through a plant canopy, dispersal distance of diaspores with thorns or those without appendages was promoted at low wind speed (2 m s−1), while that of diaspores with low wing loading (0.5 mg mm−2) and terminal velocity (2.5 m s−1) was promoted by relatively high (6 m s−1) wind speed. A plant canopy could increase seed dispersal distance, which may be due to the complicated updraft generated by canopy. The effect of maternal plants on seed dispersal regulates the distribution pattern and the species composition of the community

The feasibility of using soil seed bank for natural regeneration of degraded sandy grasslands

Desertification in degraded grasslands is manifested through the development of bare sandy patches, which eventually lead to habitat fragmentation. The ability of these bare sandy patches to regenerate naturally through in-situ soil seed banks is not well understood. To fill this knowledge gap, we randomly selected 24 bare sandy patches with areas ranging from 19 to 898 m2 in a desertified grassland of the Horqin sandy land, Northern China to determine whether soil seed bank can be used for natural regeneration of bare sandy patches. Species composition and density of soil seed bank as well as aboveground vegetation composition, abundance and coverage were investigated. We then determined their relationships with in-situ habitat characteristics. Our observations showed that the studied area had low soil seed bank density and species richness, as well as depauperate soil seed bank communities. Consequently, local soil seed bank was not able to provide sufficient seed source for natural regeneration. This was indicated by the relationships between aboveground vegetation, soil seed bank and the in-situ habitat characteristics. For bare patches with an area between 300 m2 and 900 m2, increase the soil seed bank density and species richness should be the main restoration measures. For bare patches with a small area of less than 50 m2, restoration of vegetation density should be the main measure. Our data highlighted that different extents of desertification, indicated by different bare patches, are requiring distinct restoration measures

Geographical distribution and determining factors of different invasive ranks of alien species across China

Determination of the geographical distribution and life-form spectra of alien species with different invasive abilities are essential to understand the process of invasion and to develop measures to manage alien species. Based on six classifications of Chinese alien species, environmental and social data, we determined species density, life-form spectrum of alien species, and the relationship between species density of alien species and climatic or social factors. The species density of alien species increased from the northwest to the southeast regions of China for all the six ranks. The boundary line between low and high species density of alien species was consistent with the dividing line of population density (the “Hu Line”). Mean annual precipitation was the most important factor for species density in malignant invaders, serious invaders, local invaders, and species requiring further observation (Ranks I, II, III, and V, respectively). Gross domestic product per square kilometer and annual minimum temperature were the most important factors in mild invaders and cultivated aliens (Ranks IV and VI, respectively). Annual and biennial herbs made up 52.9% to 71.2% of total species in Ranks I to IV; shrubs and trees 3.7% to 14.7%. The annual and biennial herbs were 35.5% and 32.6%, and the shrubs and trees were 25.3% and 31.6% in Ranks IV and VI. Results implied that precipitation was the most important factor on species density for the invasive alien species. However, social factors and temperature were the most important factors for the non-invasive alien species. The invasive alien species had a high proportion of annual and biennial herbs and non-invasive alien had a high proportion of shrubs and trees. It is important to understand the geographical distribution and life-form spectra of various invasive alien species for alien species controls

Relationship between seed morphological traits and wind dispersal trajectory

The structure and dynamics of plant populations and communities are largely influenced by seed dispersal. How the wind dispersal trajectory of seeds shifts with differences in seed morphology remains unknown. We used a wind tunnel and video camera to track the dispersal trajectory of seven species of Calligonum whose seeds have different kinds of appendages and other morphological traits, using variable wind speeds and release heights to determine the relationship between seed morphological traits and wind dispersal trajectory. Concave-, straight-line-, horizontal-projectile- and projectile-shaped trajectories were found. Dispersal trajectories such as the horizontal projectile (HP) and projectile (P) tended to have a long dispersal distance. Straight line (SL) and concave curve (CC) trajectories tended to have a short dispersal distance. Seeds with bristles and large mass tended to have SL and CC trajectories, those with wings or balloon and small mass tended to have HP and P trajectories. Wind speed tended to have a stronger influence on the dispersal trajectory of light and low-wing-loading seeds, and release height tended to have a stronger influence on the dispersal trajectory of heavy and high-wing-loading seeds. Thus, seed wind dispersal trajectory is not only determined by seed morphological characteristics but also by environmental factors such as wind speed and release height

Responses of secondary wind dispersal to environmental characteristics and diaspore morphology of seven Calligonum species

Secondary diaspore dispersal by wind, that is, wind‐driven movement along the ground surface (GS), is important for the structure and dynamics of plant populations and communities. However, how wind velocity (WV), GS, and diaspore morphology influence diaspore secondary dispersal by wind are unclear. We used a wind tunnel and video camera to measure the threshold of WV (TWV) and diaspore velocities (DV) of secondary diaspore dispersal. Diaspores of seven Calligonum species with different appendages (wings, bristles, membranous balloon, and wings + thorns) were used to determine the TWV and DV under variable wind speed (4, 6, 8, and 10 m s‐1) and four GSs (cement, sand, loam, and gravel). GS and diaspore morphological traits explained 37.1 and 18% of diaspore TWV, respectively. Meanwhile, WV, GS, and diaspore morphological traits explained 62.4, 13.6, and 3.2% of DV, respectively. An increasing trend was shown for TWV, and a decreasing trend was shown for DV in the order of cement, sand, loam, and gravel surfaces. Spherical and light diaspores had low TWV and high DV, whereas winged and heavy diaspores had high TWV and low DV. Our results indicated that adaptive features of diaspore appendages might be the result of selection for primary dispersal or secondary dispersal. The mechanism of diaspore secondary dispersal is important for understanding the recovery of degraded sand dunes and providing theoretical support for restoration practices

Mesophytic and less-disturbed mountainous habitats are important for in situ conservation of rare and endangered plants

Protecting rare and endangered plants is important for maintaining ecosystem structure and function, conserving biodiversity, and even sustaining national economic growth. However, the effects of habitat characteristics, geographical distribution, and climatic factors on the distribution of rare and endangered plants in China, home to 19.4 % of the world’s endangered species, remain unclear. To address this important knowledge gap, we collected information on climate, altitude, habitat, and distribution of rare and endangered plants in China to determine their habitat characteristics, geographical distribution, and the relationships between environmental factors and species density. We found that rare and endangered plants tend to occur in warm, humid, and forested habitats. Mountains, rather than plains, hills, eolian landforms, tablelands, lakes, and glaciers, can provide mesophytic and less-disturbed refuges for rare and endangered plants. In particular, medium and medium high-altitude mountains located in monsoon dominated regions with high precipitation, temperature, and humidity provide habitats for species of rare and endangered plants with high density. Our findings highlight the importance for a more explicit consideration of these mountains for in situ conservation of rare and endangered plants

Effects of climatic and social factors on dispersal strategies of alien species across China

Determination of dispersal strategies of alien species and its relationship with social and climatic factors are essential to understand the mechanisms of species invasion and adaption. Based on morphological trait, dispersal mode, and dispersal agent of diaspore of 562 alien species across China, we determined: (i) the proportions of five dispersal strategies (i.e., autochory, anemochory, hydrochory, zoochory, and anthropochory), (ii) the relationships between the dispersal strategies and socio-climatic factors in 34 administrative regions across China, and (iii) the correlations between different dispersal strategies. Anthropochory, zoochory, and anemochory account for nearly 90.0% of all the dispersal strategies of alien species. Mean frost days (MFD), mean annual humidity (MAH), and gross domestic product (GDP) were the main climatic and social factors that were correlated to different dispersal strategies. Zoochory was positively related to MFD, but negatively related to the autochory and anthropochory. MAH negatively influenced the anemochory, while GDP positively influenced the hydrochory. We classified the six dispersal strategies into two groups based on the correlations among dispersal strategies, group I included autochory and anthropochory, and group II included anemochory, hydrochory, and zoochory. Within a group, dispersal strategies were positively correlated, while between groups, dispersal strategies were negatively correlated. Positive correlation between different strategies might be co-owned while negative correlation between different strategies might not be co-owned by one alien species. Understanding the characteristics of the dispersal strategies of alien species is important for policy makers when controlling the dispersal of malignant invasive alien species, predicting the distribution, and decreasing or cutting off the dispersal pathways of invasive alien species

The Adaptive Capacity of Alien and Rare Species in China

Alien and rare plants tend to adapt to contrasting biotic and abiotic conditions. However, adaptability assessments of alien and rare plants using biological and habitat characteristics in stressful and disturbed environments are limited. We collected and demonstrated the biological and habitat characteristics and assessed the adaptive capacity of alien and rare plants in China using the analytic hierarchy process. Biological characteristics, such as dispersal strategy, sexual and asexual reproduction modes, life form, and habitat characteristics (e.g., habitat type and distribution spatial extent), are important indicators of the adaptability of alien and rare plants to stressful and disturbed environments. Alien plants have a higher adaptive capacity to disturbed environments than rare plants, while rare plants have a higher adaptive capacity to stressful environments than alien plants. Stressful and disturbed environments constrain the adaptive capacity of alien and rare plants, respectively. However, the constraint on alien plants from stressful environments is weaker than that on rare plants from disturbed environments. Understanding the adaptive capacity of alien and rare plants will help researchers and policymakers develop strategies for preventing the invasion of alien plants as well as protecting rare and endangered plants

A video camera recording method for measuring terminal velocity of seed dispersal by wind

An accurate and convenient method is essential for measuring the terminal velocity of seeds dispersed by wind. Systematic and random errors produced by existing methods lower the accuracy and convenience in determining seed terminal velocity. In this study, a video camera was used to record the falling process of forty-one species of wind-borne seed with eight appendage structures and seven aerodynamic behaviors in a settling tower at a speed of 50 frames per second (fps). The videos were analyzed by Quick Time Player to determine seed acceleration height, acceleration time, and terminal velocity. The results showed that acceleration height and time, terminal velocity, and the difference between terminal velocity and descent velocity (DTD) increased with wing loading. Compared with dropping methods, the camera recording method eliminated the effect of acceleration and corrected seed terminal velocity. Based on wing loading, release heights were determined for accurate measurement of terminal velocity of different seeds. This method, due to its inexpensive equipment, high accuracy, easy observation and operation, can be applied to measure the terminal velocity of wind dispersed seeds, and provides a promising method in exploring the dispersal process of seeds.Fil: Liu, Minghu. Chinese Academy Of Forestry; ChinaFil: Xin, Zhiming. Chinese Academy Of Forestry; ChinaFil: Su, Zhi. Chinese Academy Of Forestry; ChinaFil: Zhao, Yingming. Chinese Academy Of Forestry; ChinaFil: Li, Xinle. Chinese Academy Of Forestry; ChinaFil: Liu, Zhimin. Chinese Academy of Sciences; República de ChinaFil: Cony, Mariano Anibal. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; ArgentinaFil: Liang, Wei. Chinese Academy of Sciences; República de ChinaFil: Qin, Xuanping. Chinese Academy of Sciences; República de ChinaFil: Qian, Jianqiang. Henan Agricultural University; ChinaFil: Cui, Xue. Station Of Forest And Grassland Pest Control And Quarantine; ChinaFil: Zhou, Quanlai. Chinese Academy of Sciences; República de Chin