The function of the hygroscopic awn of Themeda triandra 1

The hygroscopic awn of species such as Themeda triandra is widely believed to be a device ensuring the early burial of its seed. This belief has been extensively tested and no tendency for such self‐burial has been found. It has been demonstrated that the propelling action of the awn does cause the seed to move along the surface and its possible function as a dispersal mechanism is tentatively suggested.     

干旱胁迫及土壤埋藏深度对马桑种子萌发的影响

[目的]探讨不同干旱胁迫和土壤埋藏深度对马桑种子出苗率的影响。[方法]研究不同强度干旱(5%、10%、15%、20%、25%、30%)胁迫及不同土壤埋藏深度(0、1、2、3、5、7 cm)下马桑种子萌发指标的变化。[结果]马桑种子萌发率随着干旱胁迫的增加呈下降趋势,干旱胁迫抑制了种子萌发率和萌发速率;马桑在土壤表层出苗率最高,在≥2 cm的土壤埋藏深度下无幼苗出土。[结论]试验结果为研究马桑种子萌发行为对石漠化恶劣生境的适应机制提供了理论依据。     

高寒草地凋落物覆盖对狼毒生长微环境及种苗定居的影响

种子萌发和幼苗定居是植物生活史中最为脆弱的两个阶段。为了探明高寒草地狼毒（Stellera chamaejasme）种苗定居的生境选择,本研究在其原生境下通过人工控制试验,研究凋落物覆盖对土壤微环境（温、湿度）的影响以及狼毒种子在不同生境条件下的出苗和定居表现。结果表明：凋落物覆盖总体上能够降低土壤温度,提高土壤含水量,且能显著降低表层土壤温度和含水量的日振幅;与对照（土壤裸露）相比,凋落物覆盖显著降低狼毒种子的出苗率和成苗率,但对其越冬存活率的影响并不显著;土壤埋深对狼毒种子的出苗产生显著影响,埋植于表层土壤（< 0.5 cm）的狼毒种子其出苗率和越冬成活率均显著高于深层土壤（2 cm和4 cm）的种子。分析表明,高寒草地凋落物的存在或种子埋植太深均不利于狼毒种苗的定居;因此,草地裸露或促使土壤浅表化的扰动均可促进狼毒种群建立,是导致退化草地狼毒种群扩散的主要生态因素。     

Germination ecology of nutraceutical herbs for agronomic perspectives

The growing need for nutraceutical foods has elicited increasing interest in the herbs traditionally used for ethnobotanical purposes. Their richness in antioxidants inspired this research, which is aimed at cultivating them as crops. Sixteen wild species of crucial interest as food were studied in term of seed propagation. The frequent dormancy was reduced or removed by physical, or physiological seed treatments in laboratory experiments in Petri dishes. However, their direct field sowing, in spring and autumn, did not show the same performance in spite of the efficacy of the treatments. This specially occurs in the case of species with very small seeds suggesting a burial involvement of this soil-mediated inhibition. This inhibition was markedly lower after greenhouse sowing in a soft substrate (peat–pearlite) confirming the hypothesis that the soil acts (via hypoxia) as a crucial obstacle to germination. The study of the emergence reduction by a slight burial (1 cm), compared to unburied germination, allowed to evaluate, for each species, the burial-mediated inhibition. After the 1000 seed weight measurement a relation between these two parameters (burial inhibition and seed weight) was fitted. A polynomial regression confirmed the inverse relationship between seed weight and burial-mediated inhibition showing the remarkable burial-intolerance of very small seeds. Consequently the greenhouse sowing in substrate appears the most suitable agronomic strategy overall for food herbs characterized by little seeds. Critical issues are discussed regarding these weeds becoming real nutraceutical crops.     

Microbial decomposition of skeletal muscle tissue (Ovis aries) in a sandy loam soil at different temperatures

A laboratory experiment was conducted to determine the effect of temperature (2, 12, 22 °C) on the rate of aerobic decomposition of skeletal muscle tissue (Ovis aries) in a sandy loam soil incubated for a period of 42 days. Measurements of decomposition processes included skeletal muscle tissue mass loss, carbon dioxide (CO₂) evolution, microbial biomass, soil pH, skeletal muscle tissue carbon (C) and nitrogen (N) content and the calculation of metabolic quotient (qCO₂). Incubation temperature and skeletal muscle tissue quality had a significant effect on all of the measured process rates with 2 °C usually much lower than 12 and 22 °C. Cumulative CO₂ evolution at 2, 12 and 22 °C equaled 252, 619 and 905 mg CO₂, respectively. A significant correlation (P<0.001) was detected between cumulative CO₂ evolution and tissue mass loss at all temperatures. Q₁₀s for mass loss and CO₂ evolution, which ranged from 1.19 to 3.95, were higher for the lower temperature range (Q₁₀(2-12 °C)>Q₁₀(12-22 °C)) in the Ovis samples and lower for the low temperature range (Q₁₀(2-12 °C)<Q₁₀(12-22 °C)) in the control samples. Metabolic quotient and the positive relationship between skeletal muscle tissue mass loss and cumulative CO₂ evolution suggest that tissue decomposition was most efficient at 2 °C. These phenomena may be due to lower microbial catabolic requirements at lower temperature.     

Burial of soil-surface artifacts in the presence of lumbricid earthworms

Rings of wire placed on the soil surface of two pastures containing populations of Lumbricidae were recovered after 52 months. They had been buried at the rate of 9–10 mm per year. At a forest site where only Megascolecidae were present there was no burial. At the pasture sites, populations of Lumbricidae in tubes of soil sterilized with methyl bromide 52 months earlier were indistinguishable from those in untreated soils.     

Ecological studies on Echinochloa crus-galli and the implications for weed management in direct-seeded rice

Echinochloa crus-galli, a C₄ grass, is one of the world’s most serious weeds. Weed management decisions for this species can be derived from knowledge of its seed biology. Studies were conducted to determine the effects of light on germination; seed burial depth and rice residue on emergence and growth; and flooding time and depth on emergence, survival and growth of this species. Light stimulated seed germination but it was not an absolute requirement for germination. The proportion of seeds germinating was greatest for seeds placed on the soil surface (92%), and emergence declined with increasing burial depth in soil; no seedlings emerged from the depth of 8 cm. A burial depth of only 0.4 cm reduced seedling emergence by 50%. Seedling emergence and seedling biomass were reduced by the addition of high level (6 ton ha⁻¹) of rice residue to the soil surface. Early and deep flooding significantly suppressed growth of E. crus-galli seedlings. In flooded conditions, with increased water depth the weed allocated more biomass to shoots at the expense of roots. The information gained from this study could contribute to improve weed control approaches. Soil inversion by tillage to bury weed seeds below their maximum depth of emergence, use of crop residue as mulch and early flooding of the crop could serve as important tools for managing E. crus-galli and other weed species with similar germination requirements. These management options, however, would need to be compatible with other crop management requirements.     

火棘种子萌发对干旱胁迫和土壤埋藏深度的响应

[目的]研究火棘种子萌发对干旱胁迫和土壤埋藏深度的响应.[方法]以火棘为研究对象,用PEG模拟干旱胁迫,研究种子萌发对干旱胁迫的响应特征,并对不同土壤埋藏深度下的出苗率进行测定.[结果]结果表明,火棘种子初始萌发时间和平均萌发时间均随干旱胁迫的增强而增加,种子最终萌发率随干旱胁迫的增强呈下降趋势;0 ～ 20％ PEG浓度下种子萌发;土壤对火棘种子的适宜埋藏深度为0～1 cm,最适埋深为0 cm.[结论]种子在播种前可以用适量浓度PEG溶液进行引发处理,并选择合适的播种深度以提高种子萌发率、出苗率及出苗整齐率.     

Sensitivity of Cirsium arvense to simulated tillage and competition

Abstract

Single and combined effects were studied of root length, burial depth, cutting and competition from a seasonal green manure crop on the growth and development of C. arvense from roots found in the upper soil layer. The experiment was performed under field conditions and partly repeated in a green house. The green manure consisted of a mixture of phacelia, common vetch, red clover and Italian ryegrass. Root fragments of 5 and 10 cm length were buried at 5 and 15 cm soil depth, simulating soil tillage. Use of green manure alone reduced growth of C. arvense more than any other single factor (81–99%), while root length and burial depth were more variable in their effect (0–96% reduction). Combined treatments involving both green manure, deep root burial (15 cm) and short root length (5 cm) reduced growth of C. arvense consistently by 95–100%. At the minimum regenerative capacity of C. arvense the number of leaves was 3–7 in plots with no green manure, at which time cutting had the greatest effect on regrowth the following year. The level for minimum regenerative capacity was not possible to decide for C. arvense growing in competition with green manure. Combined multiple treatments in spring, including use of green manure and mechanical operations in the upper soil layers, appear to be a potential means of reducing C. arvense infestations.