Growth Response of a Chrysanthemum Crop to the Environment. II. A Mathematical Analysis Relating Photosynthesis and Growth

Vegetative crops of chrysanthemum were grown for 5 weeks inthree replicate daylit assimilation chambers. Weekly harvestswere made from each crop for growth analysis, and on seven occasionsduring the 5-week period continuous measurements of the netCO₂ exchange rate of each crop were made over a 24 h period.A semi-empirical model for canopy photosynthesis was fittedto these data. The photosynthesis model was then incorporatedinto a simple, dynamic growth model. Using fitted values ofthe canopy photosynthesis parameters, the daily total radiationintegrals, and the experimentally observed relationship betweenthe leaf area index and crop dry matter per unit ground area,the crop growth model was used to simulate growth over the 5-weekperiod. The predicted and measured crop dry weights were inclose agreement over the whole period.     

Growth Response of a Chrysanthemum Crop to the Environment. III, Effects of Radiation and Temperature on Dry Matter Partitioning and Photosynthesis

Vegetative crops of chrysanthemum were grown for 5 or 6 weekperiods in daylit assimilation chambers. Crop responses to differentradiation levels and temperatures were analysed into effectson dry matter partitioning, specific leaf area, leaf photosynthesisand canopy light interception. The percentage of newly formed dry matter partitioned to theleaves was almost constant, although with increasing radiationor decreasing temperature, a greater percentage of dry matterwas partitioned to stem tissue at the expense of root tissue.There was a positive correlation between the percentage of drymatter in shoot material and the overall carbon: dry matterratio. Canopy photosynthesis was analysed assuming identical behaviourfor all leaves in the crop. Leaf photochemical efficiency wasonly slightly affected by crop environment. The rate of grossphotosynthesis per unit leaf area at light saturation, P_A (max),increased with increasing radiation integral, but the same parameterexpressed per unit leaf dry matter, P_w (max) was almost unaffectedby growth radiation. In contrast, P_A (max) was hardly affectedby temperature but P_w (max) increased with increasing growthtemperature. This was because specific leaf area decreased withdecreasing temperature and increased with decreasing radiation.There was a positive correlation between canopy respirationintegral and photosynthesis integral, and despite a four-foldchange in crop mass during the experiments, the maintenancecomponent of canopy respiration remained small and constant. Canopy extinction coefficient showed no consistent variationwith radiation integral but was negatively correlated with temperature.This decrease in the efficiency of the canopy at interceptingradiation exactly cancelled the increase in specific carbonassimilation rate that occurred with increasing growth temperature,giving a growth rate depending solely on the incident lightlevel. Chrysanthemum, dry matter partitioning, photosynthesis, specific leaf area     

Crop Response to Fertilizers

The response–function approach to the effects of fertilizerson crop yield is discussed. The problem is first consideredin general terms and expressions are derived for the maximumyield, the economic yield and the utilization efficiencies orrecovery factors. It is described how the use of a compoundfertilizer modifies the method. The theory is then applied tothe inverse polynomial function, which is used to describe theresponse to various levels of nitrogen, phosphorous and potassiumfertilizers; the response equation is modified to allow forthe depressive effects of high nitrogen levels on yield. Next,a numerical example is given in which the results are appliedto summer cabbage, and the most profitable fertilizer treatmentsare calculated. Finally, the application of the model acrossdifferent soils and different crops is briefly discussed. crop yield, fertilizers, mathematical model, optimal application     

A Physiological Approach to the Analysis of Crop Growth Data. II. Growth of Stylosanthes humilis

Crops of three ecotypes of the pasture legume Stylosanthes humiliswere grown during different lengths of growing season at Katherine,N T, Australia The ecotypes had contrasting flowering behaviour,and the interaction between their relative periods of vegetativeand reproductive growth and the length of the growing seasonwas studied A preliminary analysis, employing the techniques of traditionalgrowth analysis, was made of the data. The results were equivocaland a physiological approach to the analysis of the data wastaken From this second analysis it was concluded that the mainphysiological differences in the growth of the crops was theirflowering date and that differences in forage yield, and theyield of reproductive parts, at the end of the growing seasoncould be attributed to this factor No other consistent significantdifferences in the physiological behaviour of the crops wereobserved crop growth, mathematical model, Stylosanthes humilis, legume     

Allometric Growth Studies of the Carrot Crop: II. Effects of Cultural Practices and Climatic Environment

A series of experiments showed that in the carrot plant, theratio of relative growth rates of roots to that of the leaves,reached its maximum at intermediate plant densities, low soilmoisture deficits and when root and leaf temperature were bothclose to 18 °C. Application of soil nutrients had only aminor effect. Defoliation reduced relative root growth, butin a field experiment, the increase in foliage weight subsequentto the least severe defoliation treatments more than compensatedfor this reduction. A literature survey showed that those factorsaffecting the parameters of the allometric equation also affectedcarrot root shape and this inter-relation is attributed to thephysical constraints relating surface to volumetric growth.     

Allometric Growth Studies of the Carrot Crop: I. Effects of Plant Development and Cultivar

The allometric equation Y = aW^k was fitted to data from a fieldexperiment in which carrots were harvested at 14 weekly intervalsfrom a succession of 14 weekly sowings. Use of the allometricequation enabled more than 95 per cent of the variation in theweight of tap roots (Y), to be accounted for by reference tothe weight of leaves (W). The residual mean square error ofthe predicted root weight was less than the within-harvest meanerror. The exponent k, representing the ratio of relative growthrates of roots to that of leaves was 1.268 ± 0.019, similarto values calculated from field data from California and centralRussia. Large differences in the relative growth rate ratiowere found in the germination and flowering phases of growth,when values of k were 0.814 and -0.095 respectively. These differences,together with those found between cultivars, were associatedwith differing root shapes.     

Stomatal Response to Environment with Sesamum indicum. L

Leaf resistance of Sesamum indicum L. increased when the humidity gradient between leaf and air was increased, at moderate temperatures, even though calculated carbon dioxide concentrations within the leaf decreased slightly. Mesophyll resistance remained relatively constant when humidity gradients were changed, indicating that the increases in leaf resistance were mainly caused by reductions in stomatal aperture and that nonstomatal aspects of photosynthesis and respiration were not affected. Low carbon dioxide concentrations inside the leaf decreased but did not eliminate resistance response to the humidity gradient. Internal carbon dioxide concentrations had little effect on resistance in humid air but had moderate effects on resistance with large humidity gradients between leaf and air. Stomatal response to humidity was not present at high leaf temperatures. Effects of humidity gradients on photosynthetic and stomatal responses to temperature suggested that large humidity gradients may contribute to mid-day closure of stomata and depressions in photosynthesis.     

Mobilization and Acquisition of Sparingly Soluble P-Sources by Brassica Cultivars under P-Starved Environment I. Differential Growth Response,P-Efficiency Characteristics and P-Remobilization

Phosphorus （P） starvation is highly notorious for limiting plant growth around the globe. To combat P-starvation, plants constantly sense the changes in their environment, and elicit an elegant myriad of plastic responses and rescue strategies to enhance P-solublization and acquisition from bound soil P-forms. Relative growth responses, P-solublization and P- acquisition ability of 14 diverse Brassica cultivars grown with sparingly soluble P-sources （Rock-P （RP） and Ca3（PO4）2 （TCP）） were evaluated in a solution culture experiment. Cultivars showed considerable genetic diversity in terms of biomass accumulation, concentration and contents of P and Ca in shoots and roots, P-stress factor （PSF） and P use efficiency. Cultivars showed variable P-stress tolerance, and cultivars depicting low PSF and high P-efficiency values were better adaptable to P-starvation. In experiment 2, after initial feeding on optimum nutrition for 12 d after transplanting （DAT）, class-I （low P-tolerant （Oscar and Con-II）） and class-II （low P-sensitive （Gold Rush and RL-18）） cultivars were exposed to P-free environment for 25 d. All of the cultivars remobilized P from above ground parts to their roots during growth in P-free environment, the magnitude of which was variable in tested cultivars. P-concentrations （[P]s） at 37 DAT were higher in developing compared with developed leaves. Translocation of absorbed P from metabolically inactive to active sites in P- stressed plants may have helped class-I cultivars to establish a better rooting system, which provided a basis for enhanced P-utilization efficiency （PUE） and tolerance against P-stress. By supplying TCP and RP spatially separated from other nutrients in split root study, class-I cultivars were still able to mobilize RP and TCP more efficiently compared with class-II cultivars. To compare the growth behavior under P-stress, cultivars were grown in pots for 41 d after sowing, using a soil low in P （NaHCO3-extractable P = 3.97 mg/kg, M     

Response to Gravity by Zea mays Seedlings : I. Time Course of the Response

Gravistimulation induces an asymmetric distribution of free indole-3-acetic acid (IAA) in the cortex-epidermis of the Zea mays L. cv `Stowells Evergreen' mesocotyl within 15 minutes, the shortest time tested. IAA was measured by an isotope dilution method as the pentaflurobenzyl ester. The per cent IAA in the lower half of the mesocotyl cortex was 56 to 57% at 15, 30, and 90 minutes after stimulus initiation. Curvature is detectable in the mesocotyl within 3 minutes after beginning gravitropic stimulation. The rate of curvature of the mesocotyl increases during the first 60 minutes to a maximum of about 30° per hour. Thus, the growth asymmetry continues to increase for 45 minutes after hormone asymmetry is established.

Free IAA occurs predominantly in the stele of the mesocotyl whereas esterified IAA is mainly in the mesocotyl cortex-epidermis. This compartmentation may permit determining in which tissue the hormone asymmetry arises. Current data suggest the asymmetry originated in the stele.

     

Effects of Crop Diversity on Agroecosystem Function: Crop Yield Response

Understanding the role of diversity in the functioning of ecosystems has important implications for agriculture. Previous agricultural research has shown that crop rotation and the use of cover crops can lead to increases in yield relative to monoculture; however, few studies have been performed within the broader context of diversity–ecosystem function theory and in the absence of chemical inputs. We performed a field experiment in SW Michigan, USA, in which we manipulated the number of crop species grown in rotation and as winter cover crops over a 3-year period to test if varying the number of species in a rotation affected grain yield, a critical metric of ecosystem function in row-crops. The experimental design was unique in that no fertilizer or pesticides were used, and the only management variable manipulated was number of species in the rotation, thus providing a strong comparison to grassland diversity–ecosystem function experiments. Treatments included continuous monocultures of three row-crops, corn Zea mays L., soybean Glycine max (L.) Merr., and winter wheat Triticum aestivum L., and 2- and 3-year annual rotations with and without cover crops (zero, one, or two legume/small grain species), encompassing a range of crop diversity from one to six species. Crop yields and weed biomass were measured annually for 3 years and plant available soil nitrogen was measured over the course of the growing season in the final year of the study. In all 3 years, corn grain yield increased linearly in response to the number of crops in the rotation. Corn yields in the highest diversity treatment (three crops, plus three cover crops) were over 100% higher than in continuous monoculture and were not significantly different from the county average for each of the 3 years despite the absence of chemical inputs. Corn yields in the diversity treatments were strongly correlated with the availability of inorganic soil nitrogen, which was likely influenced by the number of different legume species (crops and cover crops) present in the rotation. In soybean and winter wheat, yield differences among crop diversity treatments were also significant, but of lower magnitude (32 and 53%, respectively), and showed little direct relationship to the number of crop species grown in a rotation. Results demonstrate that agricultural research motivated by ecological theory can provide important insights into the functioning of agroecosystems and enhance our understating of the linkages between diversity and ecosystem function. Importantly, these results suggest that reduced chemical inputs do not necessarily result in yield penalties and provide support for incorporation of crop or species diversity when determining how ecosystem services can be included in food, fiber, and biofuel production.     

Halotropism Is a Response of Plant Roots to Avoid a Saline Environment

1. Download : Download high-res image (258KB)
2. Download : Download full-size image

     

作物生长模拟模型研究和应用

作物生长模拟模型研究和应用宇振荣（北京农业大学农业生态环境系,１０００９４）ＳｔｕｄｉｅｓｏｎＣｒｏｐＧｒｏｗｔｈＭｏｄｅｌｌｉｎｇａｎｄＩｔｓＡｐｐｌｉｃａｔｉｏｎ．￥ＹｕＺｈｅｎｒｏｎｇ（ＤｅｐａｒｔｍｅｎｔｏｆＡｇｒｏ－Ｅ－ｃｏｌｏｇｉｃａｌＥ...     

Crop Specialization,Exchange and Robustness in a Semi-arid Environment

We compare the robustness of food supplies to annual variation in rainfall within two different agricultural systems: a generalist system with one type of agent who cultivates both maize and agave, and a specialist system composed of two types of agents who cultivate either maize or agave and are able to exchange. When mean rainfall is relatively high and less variable or relatively low and more variable, food supplies in the specialist system are more robust than in the generalist system. However, at intermediate levels of mean rainfall and variability, food supplies in the specialist system are less robust than those in the generalist system. Our analysis suggests that conflicts of interest and their associated costs constrain the development of specialization in some environments. When considering the robustness of social-ecological systems, it is important to consider “for whom a coupled social and ecological system is robust?”