Yankin Gabashin Tekun Arewa maso Yamma (ETNP) babban yanki ne mai ƙarfi, mai dorewa, kuma mai ƙarfi na oxygen (OMZ) wanda ya kai kusan rabin jimlar OMZs na duniya. A cikin zuciyar OMZ (zurfin mita 350-700), iskar oxygen da aka narkar yawanci tana kusa ko ƙasa da iyakar gano na'urori masu auna sigina na zamani (kimanin 10 nM). Tsauraran matakan iskar oxygen a sama da ƙasa da zuciyar OMZ suna haifar da tsarin tsaye na al'ummomin ƙwayoyin cuta waɗanda suma suka bambanta tsakanin sassan girman barbashi masu alaƙa (PA) da sassan girman rayuwa kyauta (FL). A nan, muna amfani da jerin amplicon 16S (iTags) don nazarin bambancin da rarrabawar al'ummomin prokaryotic tsakanin sassan girman FL da PA da kuma tsakanin yanayin redox na yanayi. Yanayin ruwa a yankin bincikenmu ya bambanta da waɗanda aka ruwaito a baya a cikin ETNP da sauran OMZs, kamar ETSP. Yawan iskar oxygen da aka gano (kimanin 0.35 μM) sun kasance a duk faɗin zuciyar OMZ a wurin ɗaukar samfurinmu. Saboda haka, tarin nitrites da aka ruwaito galibi ga OMZ cores ba su nan, haka kuma jerin kwayoyin halittar anammox (Brocadiales genus) ba su nan.CandidatusScalindua), waɗanda aka fi samu a cikin iyakokin oxic-anoksic a cikin wasu tsarin. Duk da haka, rarrabawar ƙwayoyin cuta na ammonia-oxidizing (AOB) da archaea (AOA) da kuma matsakaicin ƙimar assimilation na carbon autotrophic (1.4 μM C d)–1) ya yi daidai da matsakaicin yawan ammonium kusa da saman OMZ core. Bugu da ƙari, membobin wannan nau'inNitrospina, wani yanki mai ƙarfi na ƙwayoyin cuta na nitrite-oxidizing (NOB) ya kasance yana nuna cewa duka oxidation na ammonia da nitrite suna faruwa ne a cikin yawan oxygen da aka gano. Binciken gwajin kamanceceniya (ANOSIM) da Non-metric Dimensional Scaling (nMDS) ya nuna cewa wakilcin ƙwayoyin cuta da na archaeal phylogenetic sun bambanta sosai tsakanin sassan girma. Dangane da bayanan ANOSIM da iTag, abun da ke cikin tarin PA bai yi tasiri sosai ba ta hanyar tsarin biogeochemical mai dogaro da zurfin fiye da ɓangaren FL. Dangane da kasancewar AOA, NOB da oxygen mai kama a cikin OMZ core, muna ba da shawarar cewa nitrification tsari ne mai aiki a cikin zagayowar nitrogen na wannan yanki na ETNP OMZ.
Gabatarwa
Dangane da sauyin yanayi da ayyukan ɗan adam na gida, yawan iskar oxygen da ke narkewa yana raguwa a cikin teku mai buɗewa da kuma tsarin ruwa na bakin teku (Breitburg da sauransu, 2018). An kiyasta asarar iskar oxygen daga teku a cikin shekaru 60 da suka gabata ya wuce kashi 2% (Schmidtko da sauransu, 2017), yana haifar da damuwa game da sakamakon faɗaɗa yankin da iskar oxygen ta ƙare (Paulmier da Ruiz-Pino, 2009). Buɗaɗɗen teku OMZs suna samuwa lokacin da babban samar da iskar oxygen a saman ruwa mai yawa ya haifar da buƙatar iskar oxygen a cikin ruwan ƙarƙashin ƙasa wanda ya wuce ƙimar iskar oxygen a zurfin. Yawan iskar oxygen a cikin ginshiƙan ruwa na OMZ na iya samun tsauraran matakai (oxycline) sama da ƙasa da tsakiyar da oxygen ya ƙare, wanda ke haifar da hypoxic (yawanci tsakanin 2 da ~90 μM), suboxic (<2 μM) da anoxic (ƙasa da iyakokin ganowa (~10 nM) yadudduka masu girma dabam-dabam (Bertagnolli da Stewart, 2018). Rarrabuwar iskar oxygen yana haifar da tsarin tsaye na al'ummomin metazoan da ƙwayoyin cuta da kuma hanyoyin biogeochemical tare da waɗannan manyan oxyclines (Belmar da sauransu, 2011).
An sami mafi girman asarar nitrogen a cikin OMZs na Gabashin Tropical North Pacific (ETNP) da Kudancin Pacific (ETSP) (Calbeck da sauransu, 2017;Penn da sauransu, 2019), yankin Cariaco mai tsari na dindindin (Montes da sauransu, 2013), Tekun Larabawa (Ward da sauransu, 2009), da kuma OMZ na tsarin haƙa Benguela (Kuypers da sauransu, 2005A cikin waɗannan tsarin, hanyoyin ƙwayoyin cuta na denitrification na canonical (rage heterotrophic na nitrate zuwa tsaka-tsakin nitrogen kuma sau da yawa zuwa iskar dinitrogen) da anammox (anaerobic ammonium oxidation) suna haifar da asarar nitrogen wanda zai iya iyakance yawan samar da farko (Ward da sauransu, 2007Bugu da ƙari, fitar da sinadarin nitrous oxide na teku (mai ƙarfi a cikin iskar gas mai gurbata muhalli) daga ƙwayoyin cuta masu narkewa waɗanda ke faruwa a cikin OMZs ana kiyasta zai iya samar da aƙalla kashi ɗaya bisa uku na fitar da sinadarin nitrous oxide na halitta a duniya (Naqvi da sauransu, 2010).
ETNP OMZ babban yanki ne mai ɗorewa, mai ɗorewa, kuma mai ƙarfi wanda ya kai kusan rabin jimlar yankin OMZs na duniya, yana tsakanin latitude 0-25°N da tsawon tsayi 75 da 180°W (Paulmier da Ruiz-Pino, 2009;Schmidtko da sauransu, 2017Saboda muhimmancin muhallinsu, an yi nazari sosai kan ilimin halittu da bambancin ƙwayoyin cuta na yankuna daban-daban na ETNP OMZ (misali,Beman da Carolan, 2013;Duret da sauransu, 2015;Ganesh da sauransu, 2015;Chronopoulou da sauransu, 2017;Pack da sauransu, 2015;Peng da sauransu, 2015). Nazarin da aka yi a baya sun ba da rahoton cewa iskar oxygen da aka narkar a cikin wannan tsakiyar OMZ (zurfin kimanin mita 250–750) yawanci yana kusa ko ƙasa da iyakokin ganowa na nazari (kimanin nM 10) (Tiano da sauransu, 2014;Garcia-Robledo da sauransu, 2017Duk da haka, a gefen arewa na OMZ na ETNP (wurin da aka yi nazari a kai kimanin 22°N) yawan iskar oxygen a 500 m na iya kaiwa matsakaicin shekara tsakanin 10 zuwa 20 μM (Paulmier da Ruiz-Pino, 2009; Bayanai daga World Ocean Atlas 2013)1A lokacin yakin neman zabe da aka ruwaito a nan, mun auna iskar oxygen a cikin zuciyar OMZ a isasshen yawan (0.35 μM) don tallafawa hanyoyin ƙwayoyin cuta na aerobic, kamar ammonium da nitrite oxidation, kuma mun ɗan hana wasu muhimman hanyoyin ƙwayoyin cuta na anaerobic. An gano hanyoyin ƙwayoyin cuta na aerobic a baya a cikin layukan da ba su da kyau ko kuma marasa kyau na ETNP OMZ (Peng da sauransu, 2015;Garcia-Robledo da sauransu, 2017;Penn da sauransu, 2019Duk da haka, ba a fahimci abubuwan da ke sarrafa rarrabawa da ayyukan takamaiman ƙungiyoyin ƙwayoyin cuta masu aiki a cikin OMZs ba tukuna.
Ana iya bayyana kasancewar nitrifiers inda ba za a iya gano iskar oxygen a cikin OMZ ta hanyar sauye-sauyen da aka samu kwanan nan a matsayin tsaye na oxycline saboda iskar oxygen mai tsayi, wanda zai iya haifar da matakan oxygen na ɗan lokaci a cikin OMZ cores (Muller-Karger da sauransu, 2001;Ulloa da sauransu, 2012;Garcia-Robledo da sauransu, 2017Irin waɗannan yanayi na wucin gadi na iya zama ruwan dare ta hanyar amfani da ƙwayoyin cuta masu kama da aerobic ko microaerophilic, gami da nitrifiers. Bugu da ƙari, ƙwayoyin da ke nutsewa daga epipelagic (ƙwayoyin da aka haɗa, ƙwayoyin najasa, da kayan halitta masu rikitarwa) na iya ƙunsar matakan iskar oxygen (Ganesh da sauransu, 2014Saboda haka, ana iya jigilar iskar oxygen da ƙwayoyin cuta masu kama da aerobic zuwa ruwan da ba ya ɗauke da sinadarai masu guba, wanda ke ba da damar metabolism na aerobic ya faru na ɗan lokaci tare da ƙwayoyin cuta. An san ƙwayoyin cuta a matsayin wuraren da ƙwayoyin cuta ke yin biogeochemical cyclic cyclic (Simon da sauransu, 2002;Ganesh da sauransu, 2014) kuma yana iya tallafawa bambancin hanyoyin ƙwayoyin cuta masu kama da anaerobic ko aerobic waɗanda ba a lura da su a cikin yanayin rayuwa mai 'yanci ba (Alldredge da Cohen, 1987;Wright da sauransu, 2012;Suter da sauransu, 2018).
A cikin wannan binciken, mun binciki al'ummomin prokaryotic da ke mamaye arewacin OMZ na ETNP da abubuwan muhalli waɗanda wataƙila ke shafar rarrabawarsu ta tsaye ta amfani da jerin amplicon 16S (iTags) tare da ƙididdigar bambance-bambance masu yawa. Mun binciki ɓangarorin girma guda biyu; ɓangaren rayuwa mai 'yanci (0.2–2.7 μm), da ɓangaren da ke da alaƙa da barbashi (>2.7 μm, suna kama barbashi da ƙwayoyin protistan) a zurfin da yawa tare da oxycline wanda ya dace da yanayin redox daban-daban.
Za mu iya samar da na'urori masu auna iskar oxygen da aka narkar tare da sigogi daban-daban, don a iya sa ido kan yawan kwayoyin halitta a ainihin lokaci. Barka da zuwa tuntuɓar mu
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