The Effect of Wind and a Reduced Supply of Phosphorus and Nitrogen on the Growth and Water Relations of Festuca arundinacea Schreb

Festuca arundinaceae was grown at high and low wind-speed attwo levels of either soil phosphorus or soil nitrogen. At increasedwind-speed, mean relative growth rate and leaf extension ratewere reduced when plants were grown with high nutrient concentrationsand further reduced when phosphorus or nitrogen stress was imposedon the plants. Transpiration was increased at high wind-speedexcept under conditions of phosphorus stress, where the ratewas actually decreased. Relationships between water stress,wind and nutrient status are discussed, especially in relationto the possible role of phosphorus stress in causing sclerophylly. Festuca arundinacea Schreb., relative growth rate, water stress, wind, nitrogen, phosphorus, sclerophylly     

Imaging spectroscopy reveals the effects of topography and logging on the leaf chemistry of tropical forest canopy trees

Logging, pervasive across the lowland tropics, affects millions of hectares of forest, yet its influence on nutrient cycling remains poorly understood. One hypothesis is that logging influences phosphorus (P) cycling, because this scarce nutrient is removed in extracted timber and eroded soil, leading to shifts in ecosystem functioning and community composition. However, testing this is challenging because P varies within landscapes as a function of geology, topography and climate. Superimposed upon these trends are compositional changes in logged forests, with species with more acquisitive traits, characterized by higher foliar P concentrations, more dominant. It is difficult to resolve these patterns using traditional field approaches alone. Here, we use airborne light detection and ranging‐guided hyperspectral imagery to map foliar nutrient (i.e. P, nitrogen [N]) concentrations, calibrated using field measured traits, over 400 km² of northeastern Borneo, including a landscape‐level disturbance gradient spanning old‐growth to repeatedly logged forests. The maps reveal that canopy foliar P and N concentrations decrease with elevation. These relationships were not identified using traditional field measurements of leaf and soil nutrients. After controlling for topography, canopy foliar nutrient concentrations were lower in logged forest than in old‐growth areas, reflecting decreased nutrient availability. However, foliar nutrient concentrations and specific leaf area were greatest in relatively short patches in logged areas, reflecting a shift in composition to pioneer species with acquisitive traits. N:P ratio increased in logged forest, suggesting reduced soil P availability through disturbance. Through the first landscape scale assessment of how functional leaf traits change in response to logging, we find that differences from old‐growth forest become more pronounced as logged forests increase in stature over time, suggesting exacerbated phosphorus limitation as forests recover.     

Nutrient Addition Differentially Affects Soil Carbon Sequestration in Secondary Tropical Dry Forests: Early‐ versus Late‐Succession Stages

There is considerable interest in the potential use of soils to sequester carbon for climate change mitigation. As such, there is a need to evaluate the potential for carbon accumulation in tropical regions. We compared the effects of three annual additions of nitrogen and/or phosphorus on soil carbon and nitrogen contents and pools (bulk soil, macro‐, meso‐, and microaggregates) of two regenerating secondary tropical dry forest differing in nutrient status and succession stage (10‐year‐old early‐succession stage and approximately 60‐year‐old late‐succession stage). The selected forest sites were located on a shallow calcareous soil in the Yucatán Peninsula (Mexico). The primary production is limited by nitrogen and phosphorus in early‐succession stage and by phosphorus in late‐succession stage. In each forest site, four independent plots (12 × 12 m²) were established, the treatments being: controls and plots fertilized during three consecutive years with nitrogen, phosphorus, or nitrogen plus phosphorus. In both forests, soil carbon and nitrogen contents were consistently high, with soil carbon:nitrogen ratios generally greater than 10. Results indicate that usually there are no significant increases of soil carbon stock associated to late succession but can be increased to 3.7 Mg·ha^?1·yr^?1 with adoption of fertilizer practices. The potential soil carbon sequestration in early‐succession forest was estimated to be 2.7 Mg·ha^?1·yr^?1, and there is no indication that fertilization improves carbon sequestration. In short, results suggest that the soil potential for carbon sequestration in these ecosystems is high and depends on the specific nutrient status of the site.     

Site fertility and leaf nutrients of sympatric evergreen and deciduous species of Quercus in central coastal California

Leaf and soil nutrient levels interact with and may each influence the other. We hypothesize that to the extent soil fertility influences the nutritional state of trees, soil fertility should correlate with summer leaf nutrient levels, whereas to the extent that trees influence soil nutrient levels, the quality of leaf litterfall should correlate with soil fertility. We examined these correlations for five sympatric oak species (genus Quercus) in central coastal California. Soil fertility, including both nitrogen and especially phosphorus, correlated significantly with summer leaf nutrient levels. In contrast, phosphorus, but not nitrogen, in the leaf litterfall correlated positively with soil nutrients. These results suggest that soil nitrogen and phosphorus influence tree nutrient levels and that leaf phosphorus, but not leaf nitrogen, influence soil fertility under the trees. Feedback between the soil and the tree for phosphorus, but not nitrogen, is apparently significant and caused by species-specific differences in leaf quality and not by litterfall quality differences within a species. We also compared functional differences between the evergreen and deciduous oak species at our study site. There were no differences in soil nitrogen and only small differences for soil phosphorus between the phenological types. Differences in leaf nutrient concentration were much more pronounced, with the evergreen species having substantially lower levels of both nitrogen and phosphorus. Evergreen species conserved more phosphorus, but not more nitrogen, than the deciduous species, but there was no consistent relationship between retranslocation and either soil nitrogen or phosphorus. These results do not support the hypothesis that evergreenness is an adaptation to low soil fertility in this system.     

Enhancement of extraplastidic oil synthesis in Chlamydomonas reinhardtii using a type‐2 diacylglycerol acyltransferase with a phosphorus starvation–inducible promoter

When cultivated under stress conditions, many plants and algae accumulate oil. The unicellular green microalga Chlamydomonas reinhardtii accumulates neutral lipids (triacylglycerols; TAGs) during nutrient stress conditions. Temporal changes in TAG levels in nitrogen (N)‐ and phosphorus (P)‐starved cells were examined to compare the effects of nutrient depletion on TAG accumulation in C. reinhardtii. TAG accumulation and fatty acid composition were substantially changed depending on the cultivation stage before nutrient starvation. Profiles of TAG accumulation also differed between N and P starvation. Logarithmic‐growth‐phase cells diluted into fresh medium showed substantial TAG accumulation with both N and P deprivation. N deprivation induced formation of oil droplets concomitant with the breakdown of thylakoid membranes. In contrast, P deprivation substantially induced accumulation of oil droplets in the cytosol and maintaining thylakoid membranes. As a consequence, P limitation accumulated more TAG both per cell and per culture medium under these conditions. To enhance oil accumulation under P deprivation, we constructed a P deprivation‐dependent overexpressor of a Chlamydomonas type‐2 diacylglycerol acyl‐CoA acyltransferase (DGTT4) using a sulphoquinovosyldiacylglycerol 2 (SQD2) promoter, which was up‐regulated during P starvation. The transformant strongly enhanced TAG accumulation with a slight increase in 18 : 1 content, which is a preferred substrate of DGTT4. These results demonstrated enhanced TAG accumulation using a P starvation–inducible promoter.     

MAP1B‐LC1 prevents autophagosome formation by linking syntaxin 17 to microtubules

In fed cells, syntaxin 17 (Stx17) is associated with microtubules at the endoplasmic reticulum–mitochondria interface and promotes mitochondrial fission by determining the localization and function of the mitochondrial fission factor Drp1. Upon starvation, Stx17 dissociates from microtubules and Drp1, and binds to Atg14L, a subunit of the phosphatidylinositol 3‐kinase complex, to facilitate phosphatidylinositol 3‐phosphate production and thereby autophagosome formation, but the mechanism underlying this phenomenon remains unknown. Here we identify MAP1B‐LC1 (microtubule‐associated protein 1B‐light chain 1) as a critical regulator of Stx17 function. Depletion of MAP1B‐LC1 causes Stx17‐dependent autophagosome accumulation even under nutrient‐rich conditions, whereas its overexpression blocks starvation‐induced autophagosome formation. MAP1B‐LC1 links microtubules and Stx17 in fed cells, and starvation causes the dephosphorylation of MAP1B‐LC1 at Thr217, allowing Stx17 to dissociate from MAP1B‐LC1 and bind to Atg14L. Our results reveal the mechanism by which Stx17 changes its binding partners in response to nutrient status.     

The effect of nitrogen and phosphorus deficiency on flavonol accumulation in plant tissues

The flavonol content of Arabidopsis thaliana and tomato seedlings was assessed in conditions of reduced nitrogen or phosphorus availability. In both systems, a significant inverse relationship was observed between nutrient availability and flavonol accumulation, with nitrogen limitation promoting the greatest increase in flavonols. A trial was established to determine the effects of decreased nitrogen and phosphorus availability on the flavonol content of leaf and fruit tissues of tomato plants (Lycopersicon esculentum cv. Chaser) in a commercial situation. Nutrients were supplied by a hydroponic system with nutrient regimes designed to provide the highest and lowest nitrogen and phosphorus levels with which it is possible to support plant growth and fruit set. Fruiting was abundant and tomato fruits were harvested at mature green, breaker and red stages of ripening; leaves were also harvested from the tops of the plants. All tissues were analysed for flavonol content using reversed‐phase high‐performance liquid chromatography. Flavonol accumulation in the leaves of mature tomato plants was found to increase significantly in response to nitrogen stress, whereas phosphorus deficiency did not elicit this response. Reduced nitrogen availability had no consistent effect on the flavonol content of tomato fruits. Phosphorus deficiency elicited an increase in flavonol content in early stages of ripening. Effects of nutrient stress on the flavonol content of tomato fruits were lost as ripening progressed. The findings suggest that nutrient status may be employed to manipulate the flavonol content of vegetative tissues but cannot be used to elevate the flavonol content of tomato fruit.     

Leaf nonstructural carbohydrate concentrations of understory woody species regulated by soil phosphorus availability in a tropical forest

Leaf soluble sugars and starch are important components of nonstructural carbohydrates (NSCs), which are crucial for plant growth, development, and reproduction. Although there is a large body of research focusing on the regulation of plant NSC (soluble sugars and starch) concentrations, the response of foliar NSC concentrations to continuous nitrogen (N) and phosphorus (P) addition is still unclear, especially in tropical forests. Here, we used a long‐term manipulative field experiment to investigate the response of leaf NSC concentrations to continuous N and P addition (3‐, 5‐, and 8‐year fertilization) in a tropical forest in southern China. We found significant species‐specific variation in leaf NSC concentrations in this tropical forest. Phosphorus addition dramatically decreased both leaf soluble sugar and starch concentrations, while N addition had no significant effects on leaf soluble sugar and starch concentrations. These results suggest that, in plants growing in P‐limiting tropical soil, leaf NSC concentrations are regulated by soil P availability rather than N availability. Moreover, the negative relationships between NSC concentrations and leaf mass per area (LMA) revealed that NSCs could supply excess carbon (C) for leaf expansion under P addition. This was further supported by the increased structural P fraction after P fertilization in our previous study at the same site. We conclude that soil P availability strongly regulates leaf starch and soluble sugar concentrations in the tropical tree species included in this study. The response of leaf NSC concentrations to long‐term N and P addition can reflect the close relationships between plant C dynamics and soil nutrient availability in tropical forests. Maintaining relatively higher leaf NSC concentrations in tropical plants can be a potential mechanism for adapting to P‐deficient conditions.     

Effect of geographical range size on plant functional traits and the relationships between plant,soil and climate in Chinese grasslands

Aim Our aim was to address the potential effect of the geographical range size of species on the relationships between plant traits, soil and climate in Chinese grasslands. Previous analyses tended to examine plant–environment relationships across many species while ignoring that species with different range sizes may respond differently to the environment. Here we hypothesized that leaf traits of narrow‐ranging species would be more strongly correlated with soil and climatic variables than those of wide‐ranging species. Location Chinese grasslands. Methods Data on leaf traits, including nitrogen and phosphorus concentrations, carbon/nitrogen ratio, nitrogen/phosphorus ratio and specific leaf area, as well as species range sizes for 208 species distributed across 178 sites in Chinese grasslands were collected. Soil and climate information for each study site was also gathered. The effects of range size on leaf traits were tested using one‐way ANOVA. Correlations between leaf traits, soil and climate were calculated for all species pooled together and for species partitioned into range size quartiles, from the first (narrowest‐ ranging 25%) to the fourth (widest‐ranging 25%). Results Narrow‐ranging species tended to occur at high altitude with lower temperature but higher soil nutrient concentrations compared with wide‐ranging species. No direct link between leaf traits and species range sizes was detected. However, patterns of leaf–soil nutrient relationships changed significantly across levels of range size. Narrow‐ranging species tended to be more sensitive to variation in soil nutrient availability than wide‐ranging species, resulting in a shift from a positive leaf–soil nutrient relationship for narrow‐ranging plants to no relationship for wide‐ranging plants. Species responses to climatic variables were unrelated to their range sizes. Main conclusions The close relationship between leaf and soil nutrients indicates a specialization of narrow‐ranging species to particular habitats whereas wide‐ranging species may be able to better withstand changes in environment such as soil fertility over a large area.     

Foliar nutrient dynamics and nutrient use efficiency in Cornus florida

Summary Growth rates and seasonal changes in foliar nitrogen, phosphorus, and calcium of Cornus florida L. (flowering dogwood) individuals were determined in three forest stands which differed in soil moisture and soil nutrient availability. Nutrient use efficiency of individual trees was measured by amount of leaf dry mass produced per unit nutrient invested, rates of nutrient resorption prior to litterfall, wood and leaf mass produced per unit nutrient turnover (=growth efficiency), projected uptake needs, and losses of nutrients to simulated throughfall leaching. Relative growth rates during this drought year, as determined by dimension analysis, were highest in the site with highest soil moisture, while 5-year average relative growth rates were highest in the most fertile site. Differences in nitrogen use efficiency were generally small, with the highest efficiencies in trees on the moistest site; in contrast, phosphorus use efficiency was consistently highest on the least fertile site. Foliar calcium levels increased throughout the year and calcium use efficiency was generally highest on the least fertile site. These data suggest that growth and nitrogen use efficiency were more strongly affected by differences in soil moisture than were phosphorus or calcium use, at least during this very dry year.     

Increased precipitation modulates the influence of nitrogen and litter inputs on the nutrient resorption proficiency rather than efficiency of <Emphasis Type="Italic">Leymus chinensis</Emphasis>

Resorption of nutrients from senescing organs is an important conservation mechanism that is usually influenced by the supply of soil nutrients and plant growth requirements. Therefore, it is likely that increases in nitrogen (N), precipitation, and litter could lead to changes in nutrient resorption because of changes in nutrients in the soil and accelerated plant growth in response to the alleviation of water limitations in arid and semiarid environments. In the current study, we investigated the effects of water, N, and litter addition on the nutrient resorption efficiency and proficiency of N and phosphorus (P) in leaves and stems of Leymus chinensis in Inner Mongolia, China. Our results showed that N addition significantly decreased the N resorption efficiency in leaves under water addition, and increased P resorption efficiency under ambient precipitation conditions. There was no apparent influence of either litter or water addition on N and P resorption efficiencies. However, N and litter addition significantly altered N and P resorption proficiencies, and these effects were modulated by water availability. Furthermore, changes in resorption proficiencies were mainly associated with alterations in the nutritional status of green organs in response to water, N and litter addition, except for leaf P. Our findings highlight the importance of increased precipitation in modulating the nutrient resorption proficiency of plants under potentially increased nutrient availability in semiarid grasslands. Therefore, global changes in precipitation and N, and corresponding litter changes could result in complex effects on plant nutrient economies and, in turn, could influence the return of nutrients to the soil.     

不同林龄刺槐叶片养分重吸收特征及其对土壤养分有效性的响应

为揭示丘陵沟壑区刺槐的养分重吸收特征及其驱动因素,研究该区不同林龄刺槐叶片全氮和全磷的浓度,以及土壤有机碳、全氮、全磷、铵态氮、硝态氮和速效磷浓度及其化学计量,分析了叶片氮磷重吸收效率与土壤养分特性之间的关系。结果表明: 植物和土壤的养分随林龄增长发生显著变化,而土壤总磷和速效磷浓度较低。氮重吸收效率随林分生长先增加后降低,范围为48.2%～54.0%,平均为48.5%;磷重吸收效率则显著增加,范围为45.2%～49.4%,平均为46.9%。氮重吸收效率与土壤氮素和氮磷比呈负向响应,而磷重吸收效率与氮磷比呈显著正相关,与土壤速效磷呈负相关。表明土壤养分有效性的变化负向驱动养分重吸收效率。由于该生境中刺槐林的固氮效应及磷限制,叶片养分重吸收策略对土壤氮磷比响应强烈。     

Sexual differences in defensive and protective mechanisms of Populus cathayana exposed to high UV‐B radiation and low soil nutrient status

Previous studies have indicated that Populus cathayana Rehder females are more sensitive and less tolerant to stressful environments than males, but it is still unknown whether there are sexual differences in defensive and protective traits under high UV‐B (HUVB) radiation and low soil nutrient status. In this study, P. cathayana was employed as a model species to investigate sex‐related physiological and biochemical responses to UV‐B radiation under different soil nutrient conditions. Cuttings were exposed to two UV‐B radiation regimes (ambient UV‐B radiation and decreased UV‐B radiation) under two soil nutrient status (topsoil and deep soil) for 100 days over one growing season. Both HUVB radiation and low soil nutrient status induced greater decreases in plant growth, dry mass accumulation, gas exchange and leaf nitrogen use efficiency in females than in males, and greater increases in lipid peroxide and antioxidant enzyme activities, and secondary defense capacities in males than in females. Moreover, sexually different responses happened also in organelle ultrastructure. Our results showed that: (1) females suffered greater negative effects and exhibited lower defense capacities than did males under HUVB radiation, low soil nutrient status and their combination; (2) low soil nutrient status reduced plant's sensitivity to HUVB radiation by increasing allocation to defense and decreasing allocation to growth compared with high soil nutrient status. These results provide evidence that sexually different tradeoffs happen between growth and defense in P. cathayana under HUVB radiation and low soil nutrient status.     

Physiological and morphological changes during short term starvation of marine bacterial islates

Three marine bacteria were examined for physiological and morphological changes in the initial phase of starvation. It was found that the starvation process was induced in a similar way irrespective of whether the cells were suspended in nutrient and energy free artificial seawater (NSS) or NSS supplemented with nitrogen and phosphorus. An initial phase of increased activity was consistent with a decreased response to added nutrients. Recovery from starvation exhibited the same response in both these starvation regimes, measured throughout the starvation period. Cells in nitrogen or phosphorus deprived starvation regimes, showed a high and rapid increased activity, followed by a delayed and more pronounced decline in respiratory activity. The initial phase of starvation also included a loss of poly--hydroybutyrate as observed by transmission electron microscopy (TEM). Two bacterial strains showed formation of small vesicles on the outer cell layer when examined by TEM. This formation and release of vesicles was related to the continuous size reduction during starvation survival. The results are discussed in terms of defining the mechanisms of initial cellular responses to nutrient deprivation.Abbreviation NSS nine salt solution     

More is not necessarily better: the impact of limiting and excessive nutrients on herbivore population growth rates

Abstract 1. The body tissues of insect herbivores contain higher concentrations of nitrogen and phosphorus than do their host plants, leading to an elemental mismatch that can limit herbivore growth, fecundity and ultimately influence population dynamics. While low nutrient availability can limit herbivore growth and reproduction, nutrient levels that exceed an organism’s nutritional requirements, i.e. an organisms’ threshold elemental ratio, can also decrease performance. 2. We conducted a laboratory experiment to examine the impacts of nitrogen and phosphorus additions on population growth rates of a phloem‐feeding insect herbivore. 3. Herbivore per capita population growth rates were highest at intermediate foliar nitrogen concentrations, indicating a performance cost on the highest nitrogen foliage. While there was no direct effect of foliar phosphorus concentration on insect performance, there was a strong and unexpected indirect effect. High soil phosphorus availability increased both foliar nitrogen concentrations and aphid tissue nitrogen, resulting in low population growth rates when both soil nitrogen and phosphorus availabilities were high. 4. In this study, experimental increases in foliar nitrogen levels led to a decrease in herbivore performance suggesting that excessive nutrient levels can limit herbivore population growth rates.     

STATE TRANSITIONS AND NONPHOTOCHEMICAL QUENCHING DURING A NUTRIENT‐INDUCED FLUORESCENCE TRANSIENT IN PHOSPHORUS‐STARVED DUNALIELLA TERTIOLECTA1

Assessments of nutrient‐limitation in microalgae using chl a fluorescence have revealed that nitrogen and phosphorus depletion can be detected as a change in chl a fluorescence signal when nutrient‐starved algae are resupplied with the limiting nutrient. This photokinetic phenomenon is known as a nutrient‐induced fluorescence transient, or NIFT. Cultures of the unicellular marine chlorophyte Dunaliella tertiolecta Butcher were grown under phosphate starvation to investigate the photophysiological mechanism behind the NIFT response. A combination of low temperature (77 K) fluorescence, photosynthetic inhibitors, and nonphotochemical quenching analyses were used to determine that the NIFT response is associated with changes in energy distribution between PSI and PSII and light‐stress‐induced nonphotochemical quenching (NPQ). Previous studies point to state transitions as the likely mechanism behind the NIFT response; however, our results show that state transitions are not solely responsible for this phenomenon. This study shows that an interaction of at least two physiological processes is involved in the rapid quenching of chl a fluorescence observed in P‐starved D. tertiolecta: (1) state transitions to provide the nutrient‐deficient cell with metabolic energy for inorganic phosphate (P_i)‐uptake and (2) energy‐dependent quenching to allow the nutrient‐stressed cell to avoid photodamage from excess light energy during nutrient uptake.     

甘南高寒草甸植物元素含量与土壤因子对坡向梯度的响应

通过测定甘南高寒草甸不同坡向条件下25科86种植物叶片氮(N)、磷(P)、钾(K)含量、有机碳(C)含量、叶片含水量和相对叶绿素(SPAD)值,以及不同坡向的土壤含水量、有机碳、全氮、全磷含量等土壤指标,分析了不同坡向植物叶片元素含量与土壤环境因子之间的关系。研究结果表明,在南坡-北坡梯度上,随着土壤含水量的增加,植物叶片P含量、叶K含量和叶片含水量显著增加,而相对叶绿素显著降低。土壤养分含量与植物叶片P、叶K含量和叶含水量显著正相关,与叶片相对叶绿素显著负相关。说明不同坡向条件下叶片养分含量受土壤因子的影响显著,土壤的水分及养分状况对植物叶片元素含量的贡献不同。土壤含水量是坡向梯度上影响植物叶片特征的最主要因子。坡向梯度上土壤含水量对植物叶片各种元素含量的影响和植物叶片含水量对不同土壤因子的响应模式支持了生长在南坡的植物能以提高水分和养分利用效率而适应南坡较为干旱和贫瘠的生境。     

Transition from P‐ to N‐limited phytoplankton growth in an artificial lake on flooded cutaway peatland in Ireland

Question: Which nutrient limits primary production in a lake created by flooding industrial cutaway peatland? Location: Clongawny Lake (53°10’N, 07°53’W), County Offaly, Ireland Methods: Nutrient concentrations in lake water and the dynamics of phytoplankton populations were monitored over a 38‐month period. The ratio of dissolved inorganic nitrogen to total phosphorus (DIN:TP) and nutrient enrichment bio‐assays were used to investigate temporal changes in nutrient limitation. Results: Primary production in the new lake was phytoplankton‐driven due to the scarcity of recolonizing macrophytes. Phytoplankton growth was initially phosphorus‐limited. The runoff of phosphate fertilizer from an adjacent coniferous forestry plantation raised the TP concentration of lake water 5.5‐fold. Consequently, the biovolume of phytoplankton increased 30‐fold, and chlorophyll‐a concentrations increased eightfold, reaching hyper‐eutrophic levels. A concurrent depletion of nitrogen in lake water reduced the DIN:TP ratio from 17.8 to 0.6, and phytoplankton growth rapidly became nitrogen‐limited. Phytoplankton composition shifted from dinoflagellates to minute, unicellular chlorophytes, with a coincident decline in species diversity. Cyanobacteria did not proliferate, most likely due to the acidic nature of the lake. Conclusions: Results illustrated the vulnerability of newly created cutaway peatland lakes to developing severe phytoplankton blooms and coincident secondary nitrogen limitation in the presence of moderate external phosphorus inputs.