The association between sorghum and N₂-fixing bacteria has been assessed only under limited conditions. We investigated biological nitrogen fixation (BNF) in situ in fifteen sorghum genotypes with dry or succulent culm types under five edaphoclimatic conditions. One randomized block experiment was established in each of five locations, from the humid to the semiarid regions of Pernambuco state, Brazil. BNF was estimated using the ¹⁵N natural abundance method by comparing the average δ¹⁵N value of each sorghum genotype with those of the reference species. High levels of productivity, up to 22 Mg shoot biomass ha⁻¹ in the 3-month cycle, were obtained where rainfall was high, and up to 5 Mg ha⁻¹ was obtained under low rainfall. The nitrogen contents showed a similar pattern as biomass production, and the genotypes with the highest productivity accumulated from 200 to 300 kg N ha⁻¹. BNF ranged from 55 to 78% of plant N in one location and from 36 to 56% in another location, but BNF did not occur in the other three locations. Although the factors that blocked effective symbiosis were not determined, symbiosis was not influenced by P or K availability. The proportion of N₂ fixation was similar in the grain-producing, dry culm genotypes and in the sugar-rich, succulent culm genotypes. The sorghum genotypes fixed N₂, reaching up to 218 kg ha⁻¹ N, without inoculation with diazotrophs. Therefore, sorghum has a high potential to fix atmospheric N₂, but the factors that block N₂ fixation must be identified for crop management planning.

中文翻译：

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N同位素特征证实了在不同的水气条件下田间生长的高粱的生物固氮作用

仅在有限的条件下评估了高粱和固定N _2的细菌之间的联系。我们调查了五个高潮气候条件下具有干或多肉茎秆类型的15个高粱基因型中的原位生物固氮（BNF）。在从巴西伯南布哥州的潮湿地区到半干旱地区的五个地方，每个地方都建立了一个随机分组实验。BNF是使用所估计的¹⁵由平均δ比较n个自然丰度方法¹⁵的每个高粱基因型的N值与所述参考物质。在高降雨的情况下，在三个月的周期内获得了高达22 Mg的芽生物量ha ^-1的高生产力，而高达5 Mg ha ^-1是在低降雨量下获得的。氮含量表现出与生物质生产相似的模式，并且具有最高生产力的基因型在200至300 kg N ha ^-1之间积累。BNF在一个位置的占植物N的55-78％，在另一位置的占36-56％，但是在其他三个位置中没有发生BNF。尽管没有确定阻碍有效共生的因素，但共生不受磷或钾有效性的影响。在产生谷物的干茎基因型和富含糖的多汁茎基因型中，N ₂固定的比例相似。高粱的基因型固定为N ₂，最高达218 kg ha ^-1N，不接种重氮菌。因此，高粱具有固定大气N ₂的高潜力，但是必须确定阻碍N ₂固定的因素才能进行作物管理规划。