Seasonal dynamics of N:P ratio stoichiometry and Ca fraction for four dominant plants in the Alxa Desert

Desert plants take on unique physiologically adaptive mechanisms in response to an adverse environment. In this study, we determined the concentrations of leaf nitrogen(N), phosphorus(P), and calcium(Ca) fraction for dominant species of Artemisia ordosica, A. frigida, Calligonum mongolicum, and Oxytropis aciphylla in the Alxa Desert and discussed seasonal changes of their leaf N:P ratio and Ca fraction. The results showed that, from May to September, the N:P ratios of A. ordosica and C. mongolicum gradually and significantly increased, while those of A. frigida, and O. aciphylla had an increase trend that was not significant; the physiologically active Ca of A. ordosica and A. frigida increased significantly,while that of C. mongolicum and O. aciphylla decreased significantly. The physiologically inert calcium of C. mongolicum increased extremely significantly, while that of others was not significant. There was a significantly positive correlation between the N:P ratio and physiologically active Ca for A. ordosica, and the N:P ratio was significantly and negatively correlated with physiologically active Ca for O. aciphylla. These findings revealed that the physiological regulation mechanism was different for the plants either in earlier stage or later stage of plant-community succession.

Evaluation on nitrogen isotopes analysis in high-C/N-ratio plants using elemental analyzer/isotope ratio mass spectrometry

Elemental analyzer/isotope ratio mass spectrometry(EA/TRMS) has been widely applied to analyze the^(15)N/^(14)N isotope composition(δ^(15)N) of plants and soils,but the δ^(15)N results may be inaccurate due to incomplete combustion of the high-C/N-ratio plant samples by EA.Therefore,it is necessary to develop a method to solve the problem of imperfect combustion.In this study,we used two methods:1) adding copper oxide powder to the samples,and 2) increasing the O_2 flow(from 100 mL min^(-1) to 200 mL min^(-1)) for the auto sampler inlet purge line of the EA.The δ^(15)N values of the plant samples became more positive and tended to be stable after complete combustion.Also,the required blank samples for each plant sample decreased with increasing amount of the added CuO powder.However,at 200 mL min^(-1) of the oxygen flow in the EA,complete combustion could not be achieved without adding copper oxide,but this was done with decreased amount of CuO powder.Therefore,mixing cupric oxide into the high-C/N-ratio samples was an efficient,simple and convenient way to solve the problem of imperfect combustion in the EA.

Features on N/P ratio of plants with different functional groups between two types of steppe in semi-arid area

The differences in nitrogen/phosphorus(N/P)ratios of different functional groups in ecology are more helpful in explaining species competition and community dynamics.Based on the functional groups of plant growth type,carbon metabolism pathway,root type and phylogenetic type,we analyzed characteristics of leaf N/P ratios of 77 species in Sanggendalai(typical grassland zone)of Zhenglan Banner,Inner Mongolia,China and 91 species in the Habahu National Nature Reserve(desertified grassland zone)in Yanchi County of Ningxia,China.The results show that the N/P ratio(16.91)of C3 plants in the desertified steppe was significantly larger than that(12.72)in the typical steppe,but there was no significant difference between the N/P ratios of C4 plants in the two zones.There was no significant difference in N/P ratios between C3 plants and C4 plants in the same zone.Similarly,the N/P ratio(16.60)of dicotyledons in desertified steppe were significantly higher than that(12.98)in typical steppe,while differences in N/P ratios between monocotyledonous plants of the two zones was not significant,and there existed no significant difference in N/P ratios between dicotyledonous and monocotyledonous plants in the same zone.The N/P ratio had significant difference between gramineous and non-gramineous plants in the typical steppe but not in the desertified steppe,but there existed no significant difference in N/P ratios among different root types of perennial herbaceous plants in the same type of steppe or between two types of steppe.Thus,different features on the N/P ratios of C3 plants and dicotyledonous plants between typical steppe and desertified steppe may lead to different growth status of plants,and the N/P ratio stoichiometric of the same plant functional group may be a foundation of the changes of a plant community.

NP配施对平茬后云南松苗木N、P、K化学计量比的影响

为了解NP配施对平茬后云南松(Pinus yunnanensis)苗木各器官N、P、K化学计量比的影响,分析云南松苗木不同器官(根、茎、叶、萌条)的ω(N)∶ω(P)、ω(N)∶ω(K)、ω(P)∶ω(K)化学计量比的季节变化特征,探讨各器官间N、P、K化学计量比的相关性及其变异来源。采用N、P二因素三水平的3×3回归设计开展不同施肥试验,并对苗木采样测定,研究NP配施对平茬后云南松根、叶、茎及其萌条N、P、K化学计量特征的影响。结果表明:平茬后云南松苗木不同器官的营养元素分配没有统一的规律,展现出丰富的变异。随着施肥季节的变化,ω(N)∶ω(P)在根、茎和萌条中逐渐下降,在叶中先下降后上升,但总体差异不大。单施N肥、P肥和NP配施均对云南松苗木生长的影响产生一定差异,总体来看NP配施更有利于促进苗木的生长,且以处理5(N_(1)P_(1))表现为极显著(P<0.01)。云南松苗木各器官N、P、K化学计量比主要受N×P交互作用的影响,其次是N,影响最小的是P。除在根和叶中ω(N)∶ω(P)与ω(N)∶ω(K)之间相关性发生改变之外,其余两两间的正负相关性均保持不变,而ω(N)∶ω(P)与ω(P)∶ω(K)、ω(N)∶ω(K)与ω(P)∶ω(K)的相关性均随着施肥季节的变化相关性发生改变,且相关系数降低,分别受P和K的调控。平茬改变植株体内的营养元素含量,不同施肥处理促使云南松各器官中N、P、K化学计量特征差异极显著(P<0.01)。NP配施可以有效缓解单施N肥、P肥对植株的限制作用,使养分处于一个平衡状态,从而满足植株对生长的需要。

颗石藻C∶N∶P比率对海洋酸化与暖化的响应及其机制

颗石藻是海洋中最重要的初级生产者之一,且能通过钙化作用产生颗粒无机碳(方解石小片,也称颗石粒)并释放CO_(2),对海洋碳循环有重要贡献。由大气CO_(2)浓度升高引起的海洋酸化与暖化对颗石藻产生重大影响,受到广泛关注。本研究主要综述海洋酸化与暖化对颗石藻的生长速率和碳(C)∶氮(N)∶磷(P)比率的单一和耦合效益的影响及其潜在机制,得出结果:海洋酸化对颗石藻生长速率的影响较小,通常增大颗石藻C∶P和N∶P比率;海洋升温通常提高颗石藻的生长速率,可能增大或减小C∶P和N∶P比率。海洋酸化降低颗石藻生长速率的最适温度;而海洋升温增加生长速率的最适CO_(2)浓度。结果表明:海洋酸化与暖化的耦合作用很可能增加颗石藻的生长速率及其对CO_(2)的吸收能力,进而增加颗石藻对海洋碳循环的贡献。

常绿阔叶林植物叶片N、P化学计量特征对毛竹扩张的响应

为从生态化学计量内平衡角度解释常绿阔叶林不同层次植物对毛竹(Phyllostachys edulis)扩张的生存响应差异性,该研究采用空间代替时间的方法,在江西井冈山国家级自然保护区沿毛竹扩张方向选取典型毛竹-常绿阔叶林界面,依次设置毛竹林、竹阔混交林和常绿阔叶林样地,比较分析了毛竹扩张方向上样地内不同乔木层、灌木层、草本层植物叶片及土壤N、P含量及比例。结果表明:(1)从毛竹林到阔叶林,土壤N含量上升,P含量下降,N∶P上升(P<0.05);乔木层树种[红楠(Machilus thunbergii)、赤杨叶(Alniphyllum fortunei)及交让木(Daphniphyllum macropodum)]叶片P含量下降,N∶P上升(P<0.05);除灌木层的红果山胡椒(Lindera erythrocarpa)外,各林分中的灌木层和草本层植物N、P含量及比例变化较小。(2)土壤N∶P与乔木层、草本层和灌木层植物叶片N∶P分布呈显著正相关、负相关与不相关。(3)在各林分中,毛竹叶片N、P含量及比例较稳定。综上认为,毛竹通过改变土壤N、P化学计量特征进行扩张,引起植物体N、P元素化学计量特征发生变化。灌木及草本植物受土壤异质性影响较小,但是乔木层植物N、P元素化学计量特征却因此失衡,这可能是阔叶林乔木层树种存亡受威胁的重要原因。

Increasing nitrogen absorption and assimilation ability under mixed NO_(3)^(–)and NH_(4)^(+) supply is a driver to promote growth of maize seedlings

Compared with sole nitrate (NO_(3)^(-)) or sole ammonium (NH_(4)^(+)) supply,mixed nitrogen (N) supply may promote growth of maize seedlings.Previous study suggested that mixed N supply not only increased photosynthesis rate,but also enhanced leaf growth by increasing auxin synthesis to build a large sink for C and N utilization.However,whether this process depends on N absorption is unknown.Here,maize seedlings were grown hydroponically with three N forms (NO_(3)^(-)only,75/25 NO_(3)^(-)/NH_(4)^(+) and NH_(4)^(+) only).The study results suggested that maize growth rate and N content of shoots under mixed N supply was little different to that under sole NO_(3)^(-)supply at 0–3 d,but was higher than under sole NO_(3)^(-)supply at 6–9 d.^(15)N influx rate under mixed N supply was greater than under sole NO_(3)^(-) or NH_(4)^(+) supply at 6–9 d,although NO_(3)^(-) and NH_(4)^(+) influx under mixed N supply were reduced compared to sole NO_(3)^(-) and NH_(4)^(+) supply,respectively.qRT-PCR determination suggested that the increased N absorption under mixed N supply may be related to the higher expression of NO_(3)^(-) transporters in roots,such as ZmNRT1.1A,ZmNRT1.1B,ZmNRT1.1C,ZmNRT1.2 and ZmNRT1.3,or NH_(4)^(+) absorption transporters,such as Zm AMT1.1A,especially the latter.Furthermore,plants had higher nitrate reductase (NR)glutamine synthase (GS) activity and amino acid content under mixed N supply than when under sole NO_(3)^(-) supply.The experiments with inhibitors of NR reductase and GS synthase further confirmed that N assimilation ability under mixed N supply was necessary to promote maize growth,especially for the reduction of NO_(3)^(-) by NR reductase.This research suggested that the increased processes of NO_(3)^(-)and NH_(4)^(+) assimilation by improving N-absorption ability of roots under mixed N supply may be the main driving force to increase maize growth.

Comparison of foliar nutrient concentrations between natural and artificial forests of Pinus sylvestris var. mongolica on sandy land, China

In order to examine the causes of degradation of Pinus sylvestris var. mongolica plantations on sandy land, the foliar concentrations of N, P, K and C were analyzed and compared between the field grown P. sylvestris var. mongolica trees from two provenances （natural forests and plantations）. The results indicated that natural tree needles had lower N, P and C concentrations, and higher K concentrations than those of plantation tree needles. For plantation tree needles, ratios of N： P, P. K and N： K increased with tree age before 45 years old; but they were not clear for the natural tree needles. Compared with the conclusions reported on Pinus spp., we found that the foliar N and P concentrations were in the optimal range for both natural and plantation tree needles. This result suggested that N or P might not be the absolute limit factors in plant nutrient for P sylvestris var. mongolica on sandy land. However, foliar K concentrations in both natural and plantation tree needles were much lower than those reported on Pinus spp. （〉4.80 g kg-1）.The N： P ratio of natural needles was in the adequate ranges, but N： P ratio of plantation needles was out of the adequate ranges. These results indicated that there was a better balanced nutrition status in the natural forest than in the plantations. If only considering the foliar nutrient concentrations of P sylvestris var. mongolica from different provenances, it might be concluded that the degradation phenomenon of P. sylvestris var. mongolica plantations was not induced by nutrition deficiency of absolute nutrients of N and P, but might be induced by other mineral nutrients or by the effectiveness of N and P nutrients. The unbalanced nutrition status and relatively quick decomposition of needles in the plantations might also contribute to the degradation.

Responses of plant community to the linkages in plant-soil C:N:P stoichiometry during secondary succession of abandoned farmlands,China

Succession is one of the central themes of ecology;however,the relationship between aboveground plant communities and underground soils during secondary succession remains unclear.In this study,we investigated the composition of plant community,plant-soil C:N:P stoichiometry and their relationships during secondary succession after the abandonment of farmlands for 0,10,20,30,40 and 50 a in China,2016.Results showed that the composition of plant communities was most diverse in the farmlands after secondary succession for 20 and 50 a.Soil organic carbon and total nitrogen contents slightly decreased after secondary succession for 30 a,but both were significantly higher than those of control farmland(31.21%-139.10%and 24.24%-121.21%,respectively).Moreover,C:N ratios of soil and microbe greatly contributed to the changes in plant community composition during secondary succession of abandoned farmlands,explaining 35.70%of the total variation.Particularly,soil C:N ratio was significantly and positively related with the Shannon-Wiener index.This study provides the evidence of synchronous evolution between plant community and soil during secondary succession and C:N ratio is an important linkage between them.

Advanced Treatment of Wastewater Treatment Plant Effluent by Using Biofilms on Filamentous Bamboo

[ Objective ] The study aimed at treating wastewater treatment plant （WWTP） effluent by using bio-film reactor with filamentous bamboo as bio-carrier. [ Method] With the aid of a continuous flow reactor, a bio-film reactor using filamentous bamboo as bio-carrier was used to treat WWTP effluent with low C/N ratio, and the removal effects of CODc,, TN （total nitrogen）, and NO3--N in the wastewater were analyzed.[ Result ] The average removal rates of CODcr, TN, and NO3- -N reached 47.7%, 23.6% and 34.5% when the C/N ratio of influent was around 2. In addi- tion, a stable bio-film was formed very well in the secondary effluent with low C/N ratio and hardly degradable organic pollutants. The pollutants could be removed effectively because of the excellent surface characteristics and compositions of filamentous bamboo. [ Conclusion] The research provides a new method to treat WWTP effluent with low C/N ratio.

Effect of nitrogen and phosphorus addition on leaf nutrient concentrations and nutrient resorption efficiency of two dominant alpine grass species

Nitrogen(N)and phosphorus(P)are two essential nutrients that determine plant growth and many nutrient cycling processes.Increasing N and P deposition is an important driver of ecosystem changes.However,in contrast to numerous studies about the impacts of nutrient addition on forests and temperate grasslands,how plant foliar stoichiometry and nutrient resorption respond to N and P addition in alpine grasslands is poorly understood.Therefore,we conducted an N and P addition experiment(involving control,N addition,P addition,and N+P addition)in an alpine grassland on Kunlun Mountains(Xinjiang Uygur Autonomous Region,China)in 2016 and 2017 to investigate the changes in leaf nutrient concentrations(i.e.,leaf N,Leaf P,and leaf N:P ratio)and nutrient resorption efficiency of Seriphidium rhodanthum and Stipa capillata,which are dominant species in this grassland.Results showed that N addition has significant effects on soil inorganic N(NO_(3)^(-)-N and NH_(4)^(+)-N)and leaf N of both species in the study periods.Compared with green leaves,leaf nutrient concentrations and nutrient resorption efficiency in senesced leaves of S.rhodanthum was more sensitive to N addition,whereas N addition influenced leaf N and leaf N:P ratio in green and senesced leaves of S.capillata.N addition did not influence N resorption efficiency of the two species.P addition and N+P addition significantly improved leaf P and had a negative effect on P resorption efficiency of the two species in the study period.These influences on plants can be explained by increasing P availability.The present results illustrated that the two species are more sensitive to P addition than N addition,which implies that P is the major limiting factor in the studied alpine grassland ecosystem.In addition,an interactive effect of N+P addition was only discernable with respect to soil availability,but did not affect plants.Therefore,exploring how nutrient characteristics and resorption response to N and P addition in the alpine grassland is important to understand nutrient use strategy of plants in terrestrial ecosystems.

Effects of N:P ratio of Artemisia ordosica on growth influenced by soil calcium carbonate

Soil calcium carbonate(CaCO_3) has a strong solid phosphorus effect, and high content of CaCO_3 can significantly reduce the effectiveness of soil phosphorus. To reveal the limiting effect of soil CaCO_3 on the growth of plants on sand land and its mechanism of plant physiology, we performed pot experiments with a two-factor randomized block design and a three-factor orthogonal design for different soil CaCO_3 content treatments using Artemisia ordosica seedlings. In the experiments, we surveyed plant height, aboveground biomass, root length and root weight and analyzed N, P concentrations and RNA content of the seedlings, and discussed the relationships between relative growth rate(RGR) of the seedlings and N:P ratio as well as RNA. Results show that, the RGRs of plant height and above-ground biomass of the seedlings decreased significantly with the increase of soil CaCO_3 content, and those for root length and root weight decreased. The RGRs of plant height and above-ground biomass of the seedlings were significantly negatively correlated with leaf N:P ratios, but significantly positively correlated with leaf RNA content and leaf P concentrations. It can be seen that soil CaCO_3 is a stress factor for the growth of A. ordosica seedlings, and the growth response of the seedlings under the influence of soil CaCO_3 is in line with the Growth Rate Hypothesis.

THE N/P RATIO IN THE NORTHERN SOUTH YELLOW SEA IN AUTUMN

Study of horizontal and vertical distributions of the N/P (nitrogen versus phosphate) atom ratio in the northern South Yellow Sea showed that the ratio varied greatly in upper waters of the investigated area and was always much greater than the theoretical Redfield ratio of 16:1 found below the thermocline zone. It was in general higher near the coast and lower in the central part. With increasing depth, the ratio became smaller and smaller. This distribution pattern is attributed to: 1) the anthropogenic influence of the surface N and P which makes the N/P ratio differ from the normal value; 2) the easy adsorption of P on particles hinders P transport to the central part; 3) below the thermocline zone, the N and P mainly come from the remineralization of the sedimented phytoplankton residues which have almost the theoretical Redfield value and; 4) the existence of the Yellow Sea Bottom Cold Water which inhibits the vertical exchange of the water.

The Inhibitory Degree Between Skeletonema costatum and Dinoflagllate Prorocentrum donghaiense at Different Concentrations of Phosphate and Nitrate/Phosphate Ratios

Interactions between Skeletonema costatum (S. costatum) and Prorocentrum donghaiense (P. donghaiiense) were inves-tigated using bi-algal cultures at different concentrations of phosphate (PO4-P) and nitrate/phosphate (N/P) ratios. Experiments were conducted under P-limited conditions and the Lotka-Volterra mathematical model was used to simulate the growth of S. costatum and P. donghaiense in the bi-algal cultures. Both of these two species were inhibited significantly in bi-algal culture. The results of the simulation showed that the inhibitory degree of S. costaum by P. donghaiense was high when the concentration of PO4-P was low (0.1μmolL-1/2 d), but that of P. donghaiense by S. costaum was high with increased PO4-P supply (0.6μmolL-1/2 d). At low concen-tration of PO4-P (0.1μmolL-1/2 d), or high concentration of PO4-P (0.6μmolL-1/2 d) with high N/P ratio (160), the interactions be-tween S. costatum and P. donghaiense were dependent on the initial cell densities of both species. At high concentration of PO4-P (0.6μmolL-1/2 d) with low N/P ratio (25 or 80), S. costatum exhibited a survival strategy superior to that of P. donghaiense. The de-gree of inhibition of P. donghaiense by S. costaum increased with elevated N/P ratio when the medium was supplemented with con-centration 0.1μmolL-1/2 d of PO4-P. The degree of inhibition to P. donghaiense by S. costaum increased with elevated N/P ratio at low concentration of PO4-P (0.1 μmolL-1/2 d). This trend was conversed at high concentration of PO4-P (0.6μmolL-1/2 d). However, the degree of inhibition of S. costaum by P. donghaiense increased with the increased N/P ratio at different PO4-P concentrations (0.1μmolL-1/2 d and 0.6μmolL-1/2 d). These results suggested that both phosphate concentration and N/P ratio affected the competition between S. costaum and P. donghaiense: P. donghaiense is more competitive in environments with low phosphate or high N/P ratio and the influence of N/P ratio on the competition was more significant with lower phosphate concentration.

Yield ratio of neutrons to protons in 12C（d,n）13N and 12C（d,p）13C from 0.6 to 3 MeV

The neutron yield in the12C(d,n)13N reaction and the proton yield in the12C(d,p)13C reaction have been measured using deuteron beams of energies 0.6-3 MeV.The deuteron beam is delivered from a 4-MeV electrostatic accelerator and bombarded on a thick carbon target.The neutrons are detected at 0°,24°,and 48°and the protons at135°in the laboratory frame.Further,the ratio of the neutron yield to the proton yield was calculated.This can be used to effectively recognize the resonances.The resonances are found at 1.4 MeV,1.7 MeV,and 2.5 MeV in the12C(d,p)13C reaction,and at 1.6 MeV and 2.7 MeV in the12C(d,n)13N reaction.The proposed method provides a way to reduce systematic uncertainty and helps confirm more resonances in compound nuclei.

Comparison of the S-, N- or P-Deprivations’ Impacts on Stomatal Conductance, Transpiration and Photosynthetic Rate of Young Maize Leaves

Seven-day-old maize (Zea mays) plants were grown hydroponically for ten days in deprived nutrient solutions against the corresponding control grown under full nutrition;the effects of S-, N- or P-deprivation on laminas’ mean stomatal conductance (gs), transpiration rate (E) and photosynthetic rate (A) were monitored, along with the impact on the laminas’ total dry mass (DM), water amount (W), length and surface area (Sa). Furthermore, a time series analysis of each parameter’s response ratios (Rr), i.e. the treatment’s value divided by the corresponding control’s one, was performed. Under S-deprivation, the Rr of laminas’ mean gs, E, and A presented oscillations within a ±15% fluctuation zone, notably the “control” zone, whilst those of laminas’ total DM, water amount, surface area, and length included oscillation during the first days and deviation later on, presenting deviation during d10. Under the N-deprivation conditions all Rr time courses except the A one, included early deviations from the control zone without recovering. The deviation from the control zone appeared at d4. Under P-deprivation, all Rr time courses represented oscillations within the control zone. P-deprivation’s patterns resembled those of S-deprivation. Compared to the one of the S-deprivation, the P-one’s oscillations took place within a broader zone. Linear relationships among the various Rr patterns were found between gs-E, gs-A, E-A, DM-W and DM-Sa. In conclusion, the impact of P-deprivation appeared in an early stage and included an alleviation action, the one of N-deprivation appeared early with no alleviation action, whilst that of S-deprivation appeared later, being rather weaker when compared to the impact of the P-deprivation’s impact.

Plant Biomass, Primary Production and Mineral Cycling of a Mixed Oak Forest in Linnebjer, Sweden

Plant biomass, primary production and mineral cycling were studied in a mixed deciduous forest (Quercus robur L., Tilia cordata L. and Corylus avellana L.) in southern Sweden. Plant biomass amount above and below ground was 201 and 37 t&middotha-1, respectively. Primary production above and below ground was an estimated 13.3 and 2.3 t&middotha-1, respectively. Carbon was the dominant element in the forest ecosystem, comprising 133 t&middotha-1. Other major elements were: N > Ca > K > Si > Mg > S > Mn > P > Fe and Na (range 1123 to 18 kg&middotha-1), followed by some trace elements. Yearly litterfall restored 6.0 t&middotha-1 organic matter or 2.3 t&middotha-1 carbon. Approximately 45% decomposed and returned to the soil during the year. Monitoring of other elements revealed that the ecosystem received inputs through dry and wet deposition, in particular 34.4 kg&middotha-1 S and 9.4 kg&middotha-1 of N yearly as throughfall. Determination of yearly biomass increase showed that the oak forest ecosystem was still in an aggradation or accumulation phase.

贵州石灰岩和砂岩地区C_4和C_3植物营养元素的化学计量对N/P比值波动的影响

陆地生态系统植物的生长受到营养元素氮(N)和磷(P)的可利用性的限制。已有的证据表明营养元素的相对丰度将控制生态系统的营养元素循环和能量流动的速度。文章提出如下假设:为了适应环境的变化,植物具有可伸缩性地调整营养元素含量的能力,也就是营养元素化学计量比值变化的能力,植物N/P比值波动的影响不仅来源于N对P的相对可利用性的变化,也来源于其他营养元素化学计量的变化,尤其是与Ca的化学计量的变化。为了验证上述假设,本研究利用3种C4植物和11种C3植物,研究了植物N/P化学计量比值的波动随N与Ca和P与Ca化学计量的变化模式:对C4植物来说,N/P比值的波动主要受生物量P与Ca化学计量变化的影响;而对C3植物来说,则同时受N与Ca和P与Ca化学计量变化的控制,它们之间的相对控制能力的大小将决定植物N/P比值波动的变化梯度,C4植物和C3植物的N/P比值的波动都要受土壤pH值的影响。本研究对了解物种丰度和N对P的相对可利用性、N与Ca,以及P与Ca的化学计量之间关系具有重要意义。