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Although split fertilizer applications have been suggested as a logical strategy to reduce nitrous oxide (N 2 O) emissions by decreasing soil nitrate concentrations, their efficacy remains unclear. A laboratory incubation experiment was performed to determine the effect of split fertilization vs. single fertilization on N 2 O emissions. The split urea application reduced the peak N 2 O emissions during the incubation period, and the cumulative N 2 O emissions were significantly reduced by 28% compared with the single fertilization, although these emissions were influenced by the N fertilizer rate and soil moisture. A higher percentage reduction in cumulative N 2 O emissions under the split fertilization occurred at the low (45%) compared with the high fertilizer rate (15%). At the low fertilizer rate (200 N), the split fertilization resulted in a significantly greater reduction in N 2 O emissions under the dry soil moisture regime (53%) compared with the wet soil moisture condition (37%). In addition, the split fertilization reduced the cumulative CO 2 emissions by 9% compared with the single fertilization. Therefore, our laboratory results suggest that the split fertilization strategy appears to be a useful method to reduce greenhouse gas emissions in an irrigated agriculture ecosystem. [ABSTRACT FROM AUTHOR]

Abstract: The absence of double fertilization and lack of endosperm formation are key embryological features of Podostemaceae, which is unique among the angiosperms. Double fertilization fails in spite of the fact that two male gametes are carried in the pollen tube and the incipient embryo sac is equipped with an egg cell and a central cell. Little is known about the proximate causes of the failure of double fertilization. The female gametophyte of Zeylanidium lichenoides, (subfamily — Podostemoideae) has a monosporic mode of development resulting in an initial four-celled/four-nucleate condition. However, the central cell degenerates before the arrival of the pollen tube in the vicinity of micropyle, thus the mature and functional female gametophyte of Z. lichenoides is ontogenically a three-celled/three-nucleate structure. It is inferred that the formation of a highly reduced female gametophyte, presumably is a result of degeneration of the central cell. [Copyright &y& Elsevier]

• In the family Podostemaceae the double fertilization does not occur-. • The mature female gametophyte is 3-nucleated, 3-celled. • The central cell degenerates before the anthesis. • Programmed cell death leads to degeneration of the central cell. • Development of the female gametophyte is of a new variant of Apinagia type. The Podostemaceae family is exceptional among angiosperms because of the absence of double fertilization, a remarkable characteristic that appears to extend to the entire family. A recent investigation of some members of the family, including Dalzellia zeylanica (Tristichoideae), Griffithella zeylanica , Polypleurum stylosum , Zeylanidium lichenoides, and Zeylanidium maheshwarii (Podostemoideae), revealed that the central cell in all of them is degenerated when the pollen tube arrives at the synergid. In the present work, we studied the ontogenetic development of the female gametophyte. We also conducted a terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and an ultrastructural transmission electron microscopy (TEM) analysis of Marathrum schiedeanum (Podostemoideae) to determine the causes of central cell degeneration. The results show that in the early stage, the female gametophyte was 4-celled and 4-nucleated, but the central cell degenerated very quickly before the start of anthesis. The reduced mature female gametophyte is 3-nucleate, 3-celled. TUNEL staining and ultrastructural TEM analysis indicated that developmental programmed cell death (PCD) mediated the degeneration of the central cell. The central cell displayed a significant quantity of vacuoles containing some cellular material, and the compact chromatin was present in the nucleus and DNA fragmentation occurred. The factors that trigger PCD in the central cell are unknown, but the test results confirm that pollination is not necessary for it to occur. The death of the central cell before pollination prevents the possibility of double fertilization and consequently results in failure to form the endosperm. [ABSTRACT FROM AUTHOR]