Transcriptomic and physiological analyses identifying Lanzhou lily(Lilium davidii var.unicolor)drought adaptation strategies

Drought stress is the main limiting plant growth factor in arid and semiarid regions.The Lanzhou lily(Lilium davidii var.unicolor)is the only sweet-tasting lily grown in these regions of China that offers highly edible,medicinal,health,and ornamental value.The Tresor lily is an ornamental flower known for its strong resistance.Plants were grown under three different drought intensity treatments,namely,being watered at intervals of 5,15,and 25 d(either throughout the study or during specific growth stages).We measured the biomass,leaf area,photosynthetic response,chlorophyll content(SPAD value),and osmoregulation of both the Lanzhou lily and the Tresor lily(Lilium‘Tresor’).Additionally,we employed RNA sequencing(RNA-Seq)and qRT-PCR to investigate transcriptomic changes of the Lanzhou lily in response to drought stress.Results showed that under drought stress,the decreasing rate in the Lanzhou lily bulb weight was lower than the corresponding Tresor lily bulb rate;the net photosynthetic rate,transpiration rate,and stomatal conductance of the Lanzhou lily were all higher compared to the Tresor lily;osmoregulation constituents,such as glucose,fructose,sucrose,trehalose,and soluble sugar,in the Lanzhou lily were comparatively higher;PYL,NCED,and ERS genes were significantly expressed in the Lanzhou lily.Under moderate drought,the biosynthesis of flavonoids,circadian rhythms,and the tryptophan metabolism pathway of the Lanzhou lily were all significant.Under severe drought stress,fatty acid elongation,photosynthetic antenna protein,plant hormone signal transduction,flavone and flavonol biosynthesis,and the carotenoid biosynthesis pathway were all significant.The Lanzhou lily adapted to drought stress by coordinating its organs and the unique role of its bulb,regulating photosynthesis,increasing osmolyte content,activating circadian rhythms,signal transduction,fatty acid elongation metabolism,and phenylalanine and flavonoid metabolic pathways,which may collectively be the main adaptation strategy and mechanisms used by the Lanzhou lily under drought stress.

The impact of land use change on soil organic carbon and labile organic carbon stocks in the Longzhong region of Loess Plateau

Land use change （LUC） is widely recognized as one of the most important driving forces of global carbon cycles. The soil organic carbon （SOC） and labile organic carbon （LOC） stores were investigated at arable land （AL）, artificial grassland （AG）, artificial woodland （AW）, abandoned arable land （AAL） and desert steppe （DS） in the Longzhong region of the Loess Plateau in Northwest China. The results showed that conversions from DS to AL, AL to AG and AL to AAL led to an increase in SOC content, while the conversion from DS to AW led to a decline. The differences in SOC content were significant between DS and AW at the 20-40 cm depth and between AL and AG at the 0-10 cm depth. The SOC stock in DS at the 0-100 cm depth was 39.4 t/hm2, increased by 28.48% after cultivation and decreased by 19.12% after conversion to AW. The SOC stocks increased by 2.11% from AL to AG and 5.10% from AL to AAL. The LOC stocks changed by a larger magnitude than the SOC stocks, which suggests that it is a more sensitive index of carbon dynamics under a short-term LUC. The LOC stocks increased at 0-20 cm and 0-100 cm depths from DS to AW, which is opposite to that observed for SOC. The proportion of LOC to SOC ranged from 0.14 to 0.20 at the 0-20 cm depth for all the five land use types, indicating low SOC dynamics. The allocation proportion of LOC increased for four types of LUC conversion, and the change in magnitude was largest for DS to AW （40.91%）. The afforestation, abandonment and forage planting on arable land led to sequestration of SOC; the carbon was lost initially after afforestation. However, the carbon sink effect after abandonment may not be sustainable in the study area.

Long-term effects of gravel―sand mulch on soil organic carbon and nitrogen in the Loess Plateau of northwestern China

Gravel-sand mulch has been used for centuries to conserve water in the Loess Plateau of north- western China. In this study, we assessed the influence of long-term （1996-2012） gravel-sand mulching of cultiv- ated soils on total organic carbon （TOC）, light fraction organic carbon （LFOC）, microbial biomass carbon （MBC）, total organic nitrogen （TON）, particulate organic carbon （POC）, mineral-associated organic carbon （MOC）, perma- nganate-oxidizable carbon （KMnO4-C）, and non-KMnO4-C at 0-60 cm depths. Mulching durations were 7, 11 and 16 years, with a non-mulched control. Compared to the control, there was no significant and consistently positive effect of the mulch on TOC, POC, MOC, KMnO4-C and non-KMnO4-C before 11 years of mulching, and these organic C fractions generally decreased significantly by 16 years. LFOC, TON and MBC to at a 0-20 cm depth in- creased with increasing mulching duration until 11 years, and then these fractions decreased significantly between 11 and 16 years, reaching values comparable to or lower than those in the control. KMnO4-C was most strongly correlated with the labile soil C fractions. Our findings suggest that although gravel-sand mulch may conserve soil moisture, it may also lead to long-term decreases in labile soil organic C fractions and total organic N in the study area. The addition of manure or composted manure would be a good choice to reverse the soil deterioration that occurs after 11 years by increasing the inputs of organic matter.

Effects of intercropping on rhizosphere soil microorganisms and root exudates of Lanzhou lily(Lilium davidii var.unicolor)

Both yield and quality of Lanzhou lily(Lilium davidii var. unicolor) are seriously affected by continuous cropping. We attempted to understand the effects of intercropping on the obstacles associated with continuous cropping of Lanzhou lily(Lilium davidii var. unicolor). The changes of rhizosphere microbial biomass and diversity in interplanting and monoculturing systems were studied by using the Illumina Hi Seq sequencing technique. The contents and composition of lily root exudates were measured by gas chromatography–mass spectrometer(GC–MS). The intercropping results of Lanzhou lily showed:(1) There was no difference in the composition of the rhizosphere soil microbes at the phylum level, but the relative abundance of the microbes decreased; and the relative abundance of harmful fungi such as Fusarium sp. increased. The relative abundance of Pleosporales sp. and other beneficial bacteria were reduced. After OTU(operational taxonomic unit)clustering, there were some beneficial bacteria, such as Chaetomium sp., in the lily rhizosphere soil in the interplanting system that had not existed in the single-cropping system. We did not find harmful bacteria that had existed in the single-cropping systm in the rhizosphere soil of interplanting system. The above results indicated that the changes of relative abundance of soil fungi and bacteria in lily rhizosphere soil was not conducive to improving the ecological structure of rhizosphere soil microbes. At the same time, the microbial composition change is very complex—beneficial and yet inadequate at the same time.(2) Root exudates provide a matrix for the growth of microorganisms. Combined with the detection of root exudates, the decrease in the composition of the root exudates of the lily was probably the reason for the decrease of the relative abundance of microbes after intercropping. At the same time, the decrease of the relative content of phenolic compounds, which inhibit the growth of microorganisms, did not increase the relative content of rhizosphere soil microorganisms. Changes in amino acids and total sugars may be responsible for the growth of Fusarium sp.. The results showed that the intercropping pattern did not noticeably alleviate the obstacle to continuous cropping of Lanzhou lily, and the change of microbial biomass and diversity was even unfavorable. However, the emergence of some beneficial bacteria, the disappearance of harmful fungi, and other changes with intercropping are in favor of alleviation of obstacles to continuous cropping of Lanzhou lily.

Influence of proximity to the Qinghai-Tibet highway and railway on variations of soil heavy metal concentrations and bacterial community diversity on the Tibetan Plateau

An understanding of soil microbial communities is crucial in roadside soil environmental assessments.The 16S rRNA se quencing of a stressed microbial community in soil adjacent to the Qinghai-Tibet Highway(QTH)revealed that the accu mulation of heavy metals(over about 10 years)has affected the diversity of bacterial abundance and microbial community structure.The proximity of a sampling site to the QTH/Qinghai-Tibet Railway(QTR),which is effectively a measure of the density of human engineering,was the dominant factor influencing bacterial community diversity.The diversity of bacterial communities shows that 16S rRNA gene abundance decreased in relation to proximity to the QTH and QTR in both alpine wetland and meadow areas.The dominant phyla across all samples were Actinobacteria and Proteobacteria.The concentration of Cr and Cd in the soil were positively correlated with proximity to the QTH and QTR(MC/WC sam pling sites),and Ni,Co,and V were positively correlated with proximity to the QTH and QTR(MA/WA sampling sites).The results presented in this study provide an insight into the relationships among heavy metals and soil microbial commu nities,and have important implications for assessing and predicting the impacts of human-induced activities from the QTH and QTR in such an extreme and fragile environment.

Effect of slow-release iron fertilizer on iron-deficiency chlorosis, yield and quality of Lilium davidii var.unicolor in a two-year field experiment

Iron deficiency chlorosis of Lilium davidii var. unicolor is often the case in practice in alkaline soils of northwest region of China. It is difficult to control iron chlorosis because of high cost and short effective work time of conventional iron fertilizers. In this study, a 2-year field experiment was conducted to evaluate the effects of two slow-release fertilizers on the suppression of iron deficiency chlorosis, soil chemical properties, and the yield and quality of L. davidii var. unicolor. Results show that both coated slow-release iron fertilizers and embedded slow-release iron fertilizer effectively controlled iron-deficiency chlorosis. The application of slow-release iron fertilizers significantly increased plant height and chlorophyll content of L. davidii var. unicolor at different growth stages. Furthermore, coated iron fertilizer application significantly increased starch, protein, soluble sugar and vitamin C content of L. davidii var. unicolor, and it also significantly improved total amino acid content, with increases in essential amino acids(Trp, Leu, Lys, Phe, Val, and Thr contents) and in nonessential amino acids(Asp, Glu, Cit, Ihs, Acc, Ala, Pro, and Cys contents). It was concluded that application of coated slow-release iron fertilizer could be a promising option for suppression of iron deficiency chlorosis and deserves further study.

Effects of gibberellic acid on tiller-bulb number and growth performance of Lilium davidii var. unicolor

Lilium davidii var.unicolor(Lanzhou lily)is an important economic crop in the northwest cold and arid regions of China.Effective regulation of tiller-bulb development and plant growth is the key to improving yield and quality of the lily.This study attempted to evaluate the effect of gibberellic acid(GA3)on tiller-bulb development and plant growth of Lanzhou lily by applying GA3 at various concentrations(0 mg/L,10 mg/L,30 mg/L,60 mg/L,and 100 mg/L)before planting and in the seedling period.Results showed that the 60-mg/L GA3 application had an inhibiting effect on tiller-bulb formation and increased the ratios of single and double bulbs but decreased the ratios of bulbs with three or more tiller bulbs,as com pared to the control(CK)and other GA3 treatments.The difference in flower number did not reach significant levels among the treatments.The tillering-related endogenous hormones IAA(indole-3-acetic acid)and Z(zeatin)content de creased,while IAA/Z increased with the 60-mg/L GA3 treatment during tiller initiation.And also,the shoot-bulb number and total daughter-bulb number decreased significantly with the 60-mg/L GA3 treatment.Furthermore,the 10-mg/L GA3 application promoted growth of Lanzhou lily significantly and resulted in an increase in plant height;bulb diameter;bulb circumference;and biomass of shoots,bulbs,fibrous roots,and the whole plant.Therefore,GA3 application is promising as a new regulation method for inhibiting tiller-bulb development and promoting bulb growth in Lanzhou lily production.

Long-term effects of gravel-sand mulch thickness on soil microbes and enzyme activities in semi-arid Loess Plateau,Northwest China

In semi-arid areas of China,gravel and sand mulch is a farming technique with a long history.In this study,a sample survey was conducted on long term gravel sand mulch observational fields in the Northwest Loess Plateau to determine the effects of long term mulch on soil microbial and soil enzyme activities.We found that after long term gravel-sand mulch,compared with bare ground,soil organic matter,alkali nitrogen,conductivity decreased,while pH and soil moisture increased.Urease,saccharase and catalase decreased with increased mulch thickness,while alkaline phosphatase was reversed.The results of Illumina MiSeq sequencing shows that after gravel-sand mulch,the bacterial and fungal community structure was different from bare land,and the diversity was reduced.Compared with bare land,the bacteria Proteobacteria and Acidobacteria abundance increased with increased thickness,and Actinobacteria was opposite.Also,at the fungal genus level,Fusarium abundance was significantly reduced,and Remersonia was significantly increased,compared with bare land.Redundancy analysis(RDA)revealed that soil environmental factors were important drivers of bacterial community changes.Overall,this study revealed some of the reasons for soil degradation after long term gravel-sand mulch.Therefore,it is recommended that the addition of exogenous soil nutrients after long term gravel-sand can help improve soil quality.

Decomposition effects of Lanzhou lily(Lilium davidii var.unicolor)flowers on soil physical and chemical properties and microbial community diversity

Timely removal of the flower is a key agricultural measure to ensure the concentrated supply of nutrients for the growth of underground bulbs and to increase the yield of lilies. Removing flowers and returning them to the field is one of the tradi‐tional ways of treatment, and field litter is formed at this time. Previous study showed that the decomposition of litter changes the soil properties. In order to study the effects of lily litter decomposition on soil physical and chemical proper‐ties and microbial structure, three treatments were set up in reference to the Decomposition Bag Method: control (CK), Lanzhou lily flower treatment (LZF), and Zhongbai No.1 flower treatment (ZBF). The effects of lily decomposition on soil physical and chemical properties and microbial community composition were studied in order to provide a scientific basis and theoretical guidance for the planting process of Lanzhou lily. The results show that the decomposition of lily flowers significantly increased the contents of soil organic matter, soil total nitrogen, soil total phosphorus and soil avail‐able potassium, and decreased soil pH. RDA shows that soil available nutrients and pH were the driving factors for the change of the soil microbial community. A short-term change of soil microenvironment caused by the decomposed lily flower is beneficial to growing the Lanzhou lily. However, under the correlation analysis of environmental factors, the long-term effects of returning the Lanzhou lily flower to the field, such as the trend of soil acidification, need to be further studied.