Leaf traits of two Mediterranean perennial tussock grass species in relation to soil nitrogen and phosphorus availability

Studying relationships of plant traits to ecosystem properties is an emerging approach aiming to understand plant's potential effect on ecosystem functioning. In the current study, we explored links between morphological and nutritional leaf traits of two Mediterranean perennial grass species Stipa tenacissima and Lygeum spartum, widely used to prevent desertification process by stabilizing sand dunes. We evaluated also relationships in terms of nitrogen (N) and phosphorus (P) availability between leaves of the investigated species and the corresponding soil. Our results showed that leaf P was very low in comparison with leaf N for the two investigated species. In fact, chlorophyll content, photosynthesis capacity and water conservation during photosynthesis are mainly linked to leaf nitrogen content. Our findings support previous studies showing that at the species levels, morphological and nutritional leaf traits were not related. On the other hand, significant relationships were obtained between soil N and leaf N for S. tenacissima (P = 0.011) and L. spartum (P = 0.033). However, leaf P was not significantly related to soil P availability for both species. We suggest that any decrease in soil N with the predicted increasing aridity may result in reduction in leaf N and thus in worst dysfunction of some biological processes levels.     

Effect of pH and phosphate on soluble soil aluminium and on growth and composition of kikuyu grass

Summary Kikuyu (Pennisetum clandestinium Hochst) grew relatively poorly on the Wollongbar krasnozem at soil pH values below 4.36. At these low pH values dry matter yields were increased by raising the pH or by application of high rates of phosphate. Both treatments decreased the concentration of soluble soil-Al on which the concentration of Al in tops was linearly dependent (r=0.95). The inverse relationship found between plant growth and Al concentration, when present in excess of ∼1.5 μg/g soil and ∼90 μg/g tops, is suggestive of Al toxicity. However, at Al concentrations causing severe yield reductions, the Ca concentration in kikuyu tops was approaching deficiency levels. The Al-Ca antagonism was further demonstrated by the reduction in Ca-uptake caused by increased concentrations of soluble soil-Al under constant conditions of exchangeable Ca and of pH. The yield-reducing effects of Al toxicity per se and Al-induced Ca deficiency are therefore confounded.     

Carbon and nitrogen content of congeneric annual and perennial grass species: relationships with growth

Seven annual-perennial pairs of grass species (six congeneric and one pair taken at random) were grown under productive conditions in the laboratory in order to investigate which plant characters were responsible for the higher relative growth rate (RGR) of annuals as compared to perennials under these conditions. The nitrogen and carbon concentrations of shoot organs and of the whole plant were higher in annuals than in perennials. This was also the case for the specific absorption rate for nitrate and nitrogen productivity (on whole plant and leaf basis). The range of RGR displayed by the 14 species was large enough (0.15–0.33d⁻¹) to examine the general relationships between RGR and the various parameters measured in the present study. RGR was positively related to plant, leaf blade and sheath nitrogen concentrations, but there was no relationship between RGR and any of the carbon concentrations. RGR also strongly correlated with specific absorption rate for nitrate and with nitrogen productivity. A new factorization of this latter parameter led to the definition of the ‘leaf nitrogen productivity’ (N_LP), which is likely to depend on photosynthetic nitrogen use efficiency. RGR was shown to be strongly correlated with N_LP, but not with the second term of the factorization, namely the proportion of plant nitrogen allocated to the leaves.     

The relation between nitrogen deficiency and leaf senescence

Because the "mobilization" of nitrogen resulting from nutritional nitrogen deficiency is also prominent during leaf senescence, the characteristics of these two syndromes were compared. Oat plants ( Avena sativa L. cv. Victory) were raised on a nutrient solution, complete except for nitrogen supply (i.e., with only the seed protein as nitrogen source), and the senescence of their leaves was compared with that of controls grown on a full nutrient solution. The N-deficient plants flowered after forming only 4 leaves and each set a single seed. The nitrogen lack affected the content of chlorophyll somewhat more than the content of the amino acids or protein nitrogen. However, spraying the plants with kinetin solution was able to retain 20–30% of the chlorophyll and protein. During senescence, the chlorophyll appears to be less stable in the N-deficient leaves than in the controls, while the protein is somewhat more stable than in the controls. Also, when the detached leaves from N-deficient plants senesced in white light or in darkness, kinetin delayed their senescence almost as effectively as that of control leaves. Most strikingly, the stomata of N-deficient leaves after detachment and floating on water were largely closed in light, just as in senescence, but could be partially induced to open by kinetin treatment. Since stomatal closure has earlier been shown to cause senescence, the characteristic syndrome of foliar nitrogen deficiency is concluded to be partly that of senescence.     

Seasonal enrichment by trace elements of kikuyu grass around heavy metals industries

Summary Samples of kikuyu grass (Pennisetum clandestinum Hochst.) taken in autumn and spring around a smelting complex show a marked seasonal enrichment by trace elements. The general deposition of metals from the atmosphere, diminishing outwards from the source, produces a matrix of highly significant correlations between all contaminating metals in grass and soil (sampled in the autumn survey). re]19751208     

The effect of age on nitrogen stress and its relation to leaf nitrogen and leaf elongation in a grass

Summary Nitrogen stress inLolium rigidum was measured 5 times during the 8 weeks following emergence.Symptoms of nitrogen deficiency appeared when the stress was greater than 40 per cent. Stresses lower than this were accurately estimated either by the concentration of total nitrogen, or free ninhydrin nitrogen in the youngest fully expanded leaf, or by a leaf elongation index.Each of these estimators could be used for diagnosis of nitrogen stress with a single calibration curve, respectively, over the following minimum periods after emergence: total nitrogen — 6 weeks; free ninhydrin nitrogen –4th to the 8th week; leaf elongation — 4th to the 9th week.Preliminary calibration tables are given for the symptom-free range of nitrogen deficiency.     

松嫩平原草甸三种植物叶片N、P化学计量特征及其与土壤N、P浓度的关系

测定了松嫩平原草甸3种主要植物羊草(Leymus chinensis)、芦苇(Phragmites communis)和尖叶胡枝子(Lespedeza hedysaroides)叶片全氮、全磷浓度,并分析了它们与土壤全氮、全磷浓度的关系.结果表明:3种植物叶片全氮浓度种间差异显著(P＜0.05),而全磷浓度种间差异不显...     

The distribution of tree and grass roots in savannas in relation to soil nitrogen and water

Here we describe the fine root distribution of trees and grasses relative to soil nitrogen and water profiles. The primary objective is to improve our understanding of edaphic processes influencing the relative abundance of trees and grasses in savanna systems. We do this at both a mesic (737 mm MAP) site on sandy-loam soils and at an arid (547 mm MAP) site on clay rich soils in the Kruger National Park in South Africa. The proportion of tree and grass fine roots at each soil depth were estimated using the δ¹³C values of fine roots and the δ¹³C end members of the fine roots of the dominant trees and grasses at our study sites. Changes in soil nitrogen concentrations with depth were indexed using total soil nitrogen concentrations and soil δ¹⁵N values. Soil water content was measured at different depths using capacitance probes. We show that most tree and grass roots are located in the upper layers of the soil and that both tree and grass roots are present at the bottom of the profile. We demonstrate that root density is positively related to the distribution of soil nitrogen and negatively related to soil moisture. We attribute the negative correlation with soil moisture to evaporation from the soil surface and uptake by roots. Our data is a snapshot of a dynamic process, here the picture it provides is potentially misleading. To understand whether roots in this system are primarily foraging for water or for nitrogen future studies need to include a dynamic component.     

Interaction of nitrogen and phosphorus nutrition in determining growth

In this paper we discuss the differences and similarities in the growth response of tomato plants to N and P limitation, and to their interaction. Two detailed growth experiments, with varied N or P supply, were conducted in order to unravel the effects of N and P limitation on growth of young tomato plants (Lycopersicon esculentum Mill.). Relative growth rate (RGR) initially increased sharply with increasing plant P concentration but leveled off at higher plant P concentrations. In contrast, RGR increased gradually with increasing plant N concentration before it leveled off at higher plant N concentrations. The relationship of RGR with organic leaf N and P showed the same shape as with total N and P concentrations, respectively. The difference in response is most likely due to the different roles of N and P in the machinery of the plant's energy metabolism (e.g., photosynthesis, respiration). Plant N concentration decreased with increasing P limitation. We show that this decrease cannot be explained by a shift in dry-mass partitioning. Our results suggest that the decrease in N concentration with increasing P limitation may be mediated by a decrease in leaf cytokinin levels and is less likely due to decreased energy availability at low P conditions. Dry-mass partitioning to the roots was closely linearly related to the leaf reduced-N concentration. However, treatments that were severely P limited deviated from this relationship.     

Copper nutrition of wheat in relation to nitrogen and phosphorus fertilization

Summary In a pot culture study, copper addition to soil increased the crop yield only in presence of nitrogen. The latter increased the utilization of both native as well as applied copper but more that of applied. It also minimised the adverse effect of applied phosphorus on copper utilization. Phosphorus at the rate 45 ppm had the tendency of decreasing copper uptake by wheat if applied without nitrogen or with its low level.     

Effect of suplemental nitrogen source and feeding frequency on nutrient supply to lambs fed a kikuyu grass (Pennisetum clandestinum) hay-based diet

Eight castrated male lambs (35 ± 4 kg live weight), fed a basal diet of kikuyu grass hay, were used in a replicated 4 × 4 Latin Square experiment with a 2 × 2 factorial arrangement of treatments to evaluate the effect of supplemental feeding frequency and source of rumen degradable N on intake, digestibility, ruminal fermentation, and microbial protein yield. Treatments were supplementation with cassava meal plus calcium caseinate or cassava meal plus urea offered at a rate of 7 g/kg live weight daily in one or two meals per day. Lambs were fed twice daily in such manner to allow ad libitum comsumption of forage. There was significant feeding frequency by N source interaction on variables of intake. In general, intake of feed components was higher (P ≤ 0.05) by lambs offered the caseinate-supplement twice daily over intake observed in lambs given the others diet treatments. Digestibility of feed components was neither affected by supplemental N source (DM, P = 0.541; OM, P = 0.585; NDF, P = 0.828) nor by feeding frequency (DM, P = 0.122; OM, P = 0.175; NDF, P = 0.591). Urinary excretion of N increased (P ≤ 0.05) in lambs supplemented twice daily whereas N retention was similar for all treatments (N source, P = 0.748; feeding frequency, P = 0.418). Microbial protein entering into the small intestine was affected by the interaction between feeding frequency and N source such as an increasing (P < 0.10) in this variable was observed when lambs received the caseinate but not the urea supplement twice daily. Efficiency of microbial protein synthesis, however, was not affected by treatments (N source, P = 0.588; feeding frequency, P = 0.334). Rumen pH averaged 6.70 and it was neither affected by N source (P = 0.827) nor by feeding frequency (P = 0.740). Ruminal concentration of ammonia N was not affected by feeding frequency (P = 0.144) while it increased (P < 0.05) when urea rather than caseinate was the supplemental N source (mean of 7.61 mg/dl vs. 6.00 mg/dl). Concentration of sugars in rumen fluid was higher (P ≤ 0.05) in lambs supplemented once a day compared to twice daily (mean of 49.4 mg/dl vs. 34.4 mg/dl) for both N sources. A significant (P ≤ 0.05) N source by feeding frequency interaction effect was observed for ruminal concentrations of α-amino N compounds. In urea treatment α-amino N concentration increased (P ≤ 0.05) in lambs receiving the supplement twice daily compared to once a day (mean of 4.59 mg/dl vs. 3.70 mg/dl) while in caseinate treatment it was higher (P ≤ 0.05) in lambs offered the supplement in one meal per day compared to twice daily (mean of 5.29 mg/dl vs. 4.07 mg/dl). In conclusion, for ruminants fed a tropical grass-based diet, starch-rich supplement containing non-protein N as N source may be offered only once a day whereas the supply of nutrients may be improved if degradable true protein is included as N source and supplement is offered in two meals per day.     

The relation between some growth parameters and yield components of rice as influenced by nitrogen level and genotype

The effects of three levels of nitrogen (0, 2 and 4 g (NH₄)₂SO₄ per pot) were evaluated in four rice varieties, differing in grain size, under flooded conditions in a tropical environment. Addition of nitrogen increased plant height and leaf number on the main culm, and hastened flowering significantly in all varieties. It also increased the dry weights of leaf, and culm plus sheath at the maximum tillering stage, anthesis and harvest. The average dry weights of both leaf, and culm plus sheath increased significantly in all varieties until anthesis. Following anthesis, the dry weights of both leaf, and culm plus sheath of the large-seeded varieties, Zhu Lian and PP₆R, further increased mainly due to emergence of the late tillers, but decreased in the small-seeded varieties, IR 747 and P₃C₂₆. During grain-filling, vars Zhu Lian and PP₆R accumulated dry matter more than the other two varieties and did not use their reserve starch present in the culm plus sheath, presumably because of the lack of demand. By contrast, current photosynthesis and ‘reserve’ contributed about 70% and 30%, respectively, of the grain yield in IR 747 and P₃C₂₆. Addition of nitrogen increased grain yield significantly in all varieties. The yield increase in IR 747 and PP₆R was essentially due to increase in grain number, but that in P₃C₂₆ and Zhu Lian was due to increases in both grain size and grain number, the latter having much greater influence. Neither the percentage of filled spikelets nor the 1000-grain weight was influenced by nitrogen addition. It was concluded that grain number is the single most important yield component in rice. Path-coefficient analysis indicated that in a breeding programme involving these four rice varieties, the cross between Zhu Lian and P₃C₂₆ would be most successful in an effort to combine high spikelet number and large grain size.     

氮磷营养因子对赤潮异弯藻生长的影响

研究了N、P营养浓度对赤潮异弯藻(Heterosigma akashiwo)生长的影响.结果表明,该藻的生长速率与N、P营养因子浓度的关系符合Monod公式.在NO₃^--N浓度达到7.5 mg·L^-1时,赤潮异弯藻开始生长;浓度为3.75～75 mg·L^-1时,赤潮异弯藻的比生长速率与NO₃^--N浓度成正比关系.N营养充足时,赤潮异弯藻的最大生长速率μ_m-n=0.3475·d^-1,K_s-n=18.91 mg·L^-1.PO₄^--P浓度为0～1.0 mg·L^-1时,赤潮异弯藻的比生长速率与P浓度成正比关系;P营养充足时,赤潮异弯藻的最大生长速率μ_m-p=0.3024·d^-1,K_s-p=0.4086 mg·L^-1.N/P达到25后藻细胞浓度达到最大,表明N/P为25时最适合赤潮异弯藻生长.赤潮异弯藻最适合在N 37.5～225.0 mg·L^-1、P 5.0～50.0 mg·L^-1、N/P=25条件下生长.     

A comparison of phosphorus and nitrogen transfer between plants of different phosphorus status

Summary This study has two objections: (1) to compare transfers of phosphorus (³²P) with nitrogen (¹⁵N) from undefoliated and defoliated mycorrhizal P-rich plants to an adjacent mycorrhizal plant and (2) to determine whether the improved nutrient status of a plant growing with a nutrient-rich plant is due primarily to movement of nutrients from roots of its nutrient-rich neighbor (= nutrient transfer) or to reduced nutrient uptake by its nutrient-rich neighbor (=shift in competition). Two plants of Plantago lanceolata were grown in a three-pot unit in which each of their root systems were split, with part in the central shared pot and part by themselves in an outside pot. There were three treatments: (1) no added P; (2) P added in the outer pot to only plant, termed the donor plant, since it might provide P to the companion plant, acting as a receiver; and (3) as in the previous treatment but the P-fertilized donor plant was also clipped. To encourage the formation of hyphal links between roots of the different plants, transfers were determined when root length densities were high (90 to 130 cm cm^-3 soil) and when 56 to 85% of the root length was infected with vesicular-arbuscular mycorrhizae. Phosphorus fertilization enhanced P but not N movement within donor plants. Regardless of treatment, N transfer from donor to receiver plants was an order of magnitude greater than P transfer and in amounts that could potentially affect plant nutrition in very infertile soils. Phosphorus transfer was very small in any of the treatments. Although P fertilization and clipping improved P status of receiver plants, P transfer was not indicated as the main reason for the improved nutrition. A shift in competition between donor and receiver plants was likely the major factor in the shift in nutrition of the receiver plants.     

The relation between nitrogen percent and dry weight of inoculated legumes

Summary Results of numerous tests of tropical and temperate legume hosts and Rhizobium strains accumulated between 1952 and 1966 were examined for a relation between N percent (y) and dry weight per plant (x). The data fitted the equation y=A–be^–cx. The most effective Rhizobium strains can be selected on the basis of dry matter yields of whole plants or plant tops only, without the need for N analyses, using statistical analyses. A previously proposed method which employs the linear relation between N-yield and dry matter yield was shown to apply only when data for strains which are not fully effective are excluded.It is postulated that symbiotically fixed N forms a different compound from that resulting from applied mineral N and that this compound cannot be remobilised before flowering.deceased     

不同坡度下植物散流-过滤带对地表股流氮磷的消除效果

在植物过滤带前设置0.8~1.2 m宽的散流带,能提高过滤带对地表股流中氮、磷营养物质的去除,发生明显增效作用。之前研究均基于平缓的坡度(4%~6%),对较倾斜坡度,设置散流带是否具有增效作用尚不清楚。研究通过在黄荆(Vitex negundo)过滤带前设置五节芒(Miscanthus floridulus)散流带,观测五节芒-黄荆和纯黄荆过滤带在5%、10%、15%坡度下对氮、磷的消除,探讨散流带在不同坡度下对过滤带的增效作用。结果表明:五节芒-黄荆和黄荆过滤带对总氮、铵氮、硝氮、总磷的去除均随坡度的增加而减小,在15%坡度下的去除效率最低;3种坡度下,五节芒-黄荆对总氮、铵氮、硝氮、总磷的消除均极显著(P0.01)或显著性(P0.05)高于黄荆过滤带,表明在较大坡度下(10%、15%),五节芒散流带对黄荆缓冲带的增效作用仍然存在。研究结果能深化植物散流-过滤带水质保护功能的认识,为农业非点源污染管理提供启示。     

The relation between moisture content and moulding in cured hay

Samples of cured hay have been stored in closed containers at relative humidities of 0–95% at temperatures varying from 5 to 25° C. A curve relating equilibrium moisture content to relative humidity of the store has been constructed and the incidence of first mould growth noted. An explanation has been suggested to account for the apparent discrepancy between earlier published work concerning the onset of moulding and conditions normally prevailing on the farm. In laboratory storage experiments temperature conditions are relatively constant, whereas with hay stacked in the open air the high atmospheric humidity in winter is offset by a lowered temperature, and the higher summer temperature is accompanied by a lower moisture content in the hay.